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Tag: Aggregate functions

An Overview of Aggregate Functions in SQL

Aggregate functions are commonly used in SQL. This article will lead you through their use and show examples of how they work. SQL aggregate functions are a useful tool, especially for creating reports. They’re not difficult to understand, especially if you have some experience with Excel or similar programs. You’ve probably used aggregate functions like SUM or AVERAGE in a spreadsheet. Even if you only occasionally use them, knowing aggregate functions can help you better understand your data and work more efficiently.

SQL Window Functions vs. SQL Aggregate Functions: Similarities and Differences

If you aren’t familiar with SQL’s window functions, you may wonder how they differ from aggregate functions. When should you use window functions? In this article, we’ll review window functions and aggregate functions, examine their similarities and differences, and see which one to choose depending on what you need to do. After you’ve tackled basic SQL, you’ll probably want to get into some of its more advanced functions. That’s great; these functions make reporting and analysis easier.

Common SQL Window Functions: Positional Functions

Positional SQL window functions deal with data's location in the set. In this post, we explain LEAD, LAG, and other positional functions. SQL window functions allow us to aggregate data while still using individual row values. We've already dealt with ranking functions and the use of partitions. In this post, we'll examine positional window functions, which are extremely helpful in reporting and summarizing data. Specifically, we'll look at LAG, LEAD, FIRST_VALUE and LAST_VALUE.

SQL Statistical Analysis Part 3: Measuring Spread of Distribution

Besides knowing the centers of a distribution in your data, you need to know how varied the observations are. In this article, we’ll explain how to find the spread of a distribution in SQL. Are you dealing with a very uniform or a very spread population? To really understand what the numbers are saying, you must know the answer to this question. In the second part of this series, we discussed how to calculate centers of distribution.

An Introduction to Using SQL Aggregate Functions with JOINs

Previously, we've discussed the use of SQL aggregate functions with the GROUP BY statement. Regular readers of the our blog will also remember our recent tutorial about JOINs. If you're a bit rusty on either subject, I encourage you to review them before continuing this article. That's because we will dig further into aggregate functions by pairing them with JOINs. This duo unleashes the full possibilities of SQL aggregate functions and allows us to perform computations on multiple tables in a single query.

A Beginner’s Guide to SQL Aggregate Functions

Aggregate functions are powerful SQL tools that compute numerical calculations on data, allowing the query to return summarized information about a given column or result set. These functions can be used in conjunction with the GROUP BY statement. Let’s see how they work using some easy examples. SQL Aggregate Functions Suppose we have users residing in a city, and we store their information in two tables. These tables and their relationship are shown below:

Useful SQL Patterns: Conditional Summarization with CASE

As you start coding in SQL, you will use some statements and techniques over and over again. We call these "SQL patterns". This series will look at the most common SQL patterns and consider how to use them. Previously, we looked at the SQL pattern of matching NULLs. This is important when you are comparing columns containing NULL values. Today, we're going to consider another SQL practice: conditional summarization with CASE operator.

NULL Values and the GROUP BY Clause

We've already covered how to use the GROUP BY clause and some aggregation functions like SUM(), AVG(), MAX(), MIN(), COUNT(). In this article, we will explain how the GROUP BY clause works when NULL values are involved. We will also explain about using NULLs with the ORDER BY clause. In SQL, NULL is a special marker used to indicate that a data value does not exist in the database. For more details, check out Wikipedia's explanation of NULL in SQL.

Tag: Avg

The SQL Coalesce Function: Handling Null Values

You may already know how to return null values in SQL. Now, we’re going to learn how to do the opposite. Though the SQL COALESCE function may seem complex, it’s actually very straightforward and useful. Let’s look at several examples of how the SQL COALESCE function can be used to work with NULL values in SQL. The Need for Coalesce in SQL Before we dive into the SQL COALESCE function in detail, you should understand how NULL values behave in expressions.

How Often Employees Are Running Late for Work: SQL Datetime and Interval SQL Arithmetic

Computing Tardiness: Date, Time, and Interval SQL Arithmetic In this article, we’re going to discuss some interesting operations we can perform with date-related data types in SQL. The SQL standard, which most relational databases comply with these days, specifies the date-related data types that must be present in relational databases. The most important of such data types are date, time, timestamp, and interval. Here’s a brief rundown of the differences between these data types:

Tag: Behind the scenes

LearnSQL Track of the Season: Creating Database Structure

New year, new challenges, and ... a new SQL Track of the Season! Start 2021 by learning SQL and data engineering. In this article, we answer frequently asked questions about our Creating Database Structure track. Maybe you haven't noticed yet that there’s an order to many LearnSQL.com courses; you can learn SQL by doing them in the right order. We call this option our ‘SQL tracks’. These are logically structured and well-thought-out learning paths that will help you take the next steps towards becoming an SQL expert.

SQL Means Business - The Way of an Engineer

Have you been wondering why some companies fail and others achieve success? It's not a matter of luck but of the right people. Łukasz Kubicki at Vertabelo deals with business and product development. I asked him how he started his adventure with programming, how an engineer got into business, and if he liked playing computer games. Here's what he said. If you were to write one sentence about yourself, what would it be?

Did You Know LearnSQL.com Has Free SQL Courses?

Who doesn't like getting something for free? Each month, we give LearnSQL.com users a bit of help in their learning journey – a free, fully interactive SQL course. Since April, we have been giving our users the opportunity to learn SQL for free. Each month, we choose one of our SQL courses and give you full access to it for that month – completely free of charge! Cool, right?

Behind the Scenes at LearnSQL.com: How Our SQL Courses Are Created

Take a peek behind the scenes and learn our secret for creating great SQL courses! Have you ever wondered how LearnSQL.com courses are created? Are we looking at a lot of hard work or just a bit of magic? Or maybe both? Here’s a hint: we rely on proven methods to create user-friendly online courses. But it’s not easy! Read on to see the 8 steps we take when creating a new SQL course.

LearnSQL Track of the Season: SQL from A to Z

During Fall 2020, our main SQL track, SQL from A to Z, will be in the spotlight. In this article, we answer the most frequently asked questions about this track. At LearnSQL.com, our SQL courses are organized into tracks. A track is a sequence of courses designed to help you achieve a specific learning goal. The courses in the track are in a recommended order that progresses from the easiest to the most challenging.

A Mathematician in the World of SQL

She has a PhD in Mathematics and over 10 years’ experience teaching mathematics and computer science at the University of Warsaw. She knows SQL better than just about anyone I’ve met. Let’s get to know Agnieszka Kozubek-Krycuń, Vertabelo’s Chief Content Officer at Vertabelo. Let's go back in time. How did your adventure with math start? I’ve always enjoyed abstract concepts and problem solving. I was fascinated by variables when we learned to solve simple equations like x+2=5 in primary school.

You Want to Learn SQL? You've Come to the Right Place!

It is difficult to list all the benefits of learning SQL. You will work faster and more efficiently with a database, you will no longer be dependent on the IT department, and you will be able to analyze the data yourself and draw appropriate conclusions, among others. Add reporting to this, and you will get a very wide range of cool and useful skills. Maybe you want to change jobs or get a promotion?

Why Take the “SQL Basics” Course at LearnSQL.com

LearnSQL.com’s interactive “SQL Basics” course teaches the foundations of SQL. Discover why we built this online course, our philosophy behind it, and what it contains! What Is SQL, and Why Should You Learn It? SQL is a language used to talk to databases, computer programs that hold data and can process it efficiently. SQL can select data from a database and perform various computations on the data, be they simple or complex.

The Man Behind LearnSQL.com

If it wasn't for this guy, LearnSQL.com would never have been created. He manages the entire company, makes strategic decisions – and talks little about himself. Who is the man behind LearnSQL.com? Meet Vertabelo CEO Jarosław Błąd. SELECT interests, early_career, advice FROM Jarek AS the_man_behind_learnsql.com WHERE answer IS NOT Null AND success IS True; If you were to write one sentence about yourself, what would it be? I think I would say that I am an ordinary, simple guy who really likes what he does.

SQL Cookbook with Recipes for Success

The internet holds a lot of information and can provide solutions to various problems. SQL users, both beginners and advanced, often turn to the internet for help with SQL queries. This article will help you find the right SQL queries to solve your problems. Learn what the SQL Cookbook is and why you should use it. You will also find a list of the most important recipes, from which you will prepare a great SQL dish with the taste of success.

Tag: Birthday

Anniversary of LearnSQL.com

Consider the period from Feb. 23, 2020 to Feb. 22, 2021. A year, 255 working days. Is that a lot of time? Well, it depends. For the LearnSQL.com Team, the time has passed blazingly fast. If someone had told us a year ago that we would be where we are now, we would have said, ‘We wish!’. We had a clear vision and a plan to create the most comprehensive SQL training platform in the world, with the best set of hands-on online SQL courses, and top-notch reading materials.

Tag: Book

Can SQL Help Solve Crossword Puzzles?

Everyone has solved crossword puzzles and has certainly had some problems finding an appropriate word. Thanks to SQL, it is ridiculously simple to quickly dispel your crossword doubts and give you the correct answers. Of course, Google is commonly known as a universal cure for many doubts, but handling the problem yourself is much more rewarding. Recently I came across some simple and interesting examples from Andrew Cumming's book "

Tag: Book review

Which SQL Books Should You Read in 2021?

Readers keep asking for books that I can recommend to complement our SQL courses. There are quite a lot of SQL books on the market, but only a few are worth your attention. See which SQL-related books to read in 2021. A while ago, I wrote an article about my favorite SQL books for 2020. I chose books about various aspects of working with databases with the goal of helping you get a clear picture of SQL in the real world.

Our 6 Favorite SQL Books for 2020

So you want to learn SQL and query databases? Great! Check out these six SQL books for an in-depth look at the language and you’ll be writing queries in no time! You take SQL courses, participate in internet discussions and forums, watch tutorials on YouTube... What else can you do to develop your skills? Sometimes it’s good to reach for old-fashioned sources of knowledge: SQL books. Which book(s) should you choose?

Book Review: “Learn SQL the Hard Way” by Zed A. Shaw

“Learn SQL the Hard Way” by Zed A. Shaw is a great ebook for those who want to learn SQL essentials. At $19.99 USD, it may seem a bit expensive for an ebook, but you’re getting a DRM-free PDF, plus a whole bunch of explanatory videos and additional files. Who should read “Learn SQL the Hard Way”? Anyone interested in SQL basics – modifying databases or selecting information. Make no mistake about it: this book focuses heavily on the practical side of database language.

LearnSQL.com Review: “SQL Cookbook” by Anthony Molinaro

Recipes that make querying easy, even for the novice. In today’s information age, we have at our fingertips almost an overabundance of teaching and information on any and every subject. In the midst of this glut of information, it can be hard to decide which is the best source for our needs. But, fear not; we are here to assist you as you navigate through decisions about books on SQL topics!

5 Books That Will Grow Your SQL Skills

Which books will help you build your database skills? We look at five awesome SQL books. There’s a common saying that “all wise men read books”. I would say that all professionals read books – particularly those related to their field. There are many books about databases and SQL; most are tied to specific vendors (DB2, Oracle, MS SQL) but there are also plenty that are vendor-neutral. In this article, I’m going to review a few books that I would recommend to SQL learners at various levels of proficiency.

Tag: Calculating

SQL Statistical Analysis Part 2: Calculating Centers of Distribution

My previous article explained how to calculate frequencies using T-SQL queries. Frequencies are used to analyze the distribution of discrete variables. Today, we’ll continue learning about statistics and SQL. In particular, we’ll focus on calculating centers of distribution. We’ll learn e.g. how to calculate the SQL median, what functions to use to calculate the SQL mode, and how to calculate various types of mean in SQL (geometric mean, harmonic mean and, of course, arithmetic mean).

SQL Statistical Analysis Part 1: Calculating Frequencies and Histograms

Database and Business Intelligence (BI) developers create huge numbers of reports on a daily basis, and data analyses are an integral part of them. If you wonder whether you can perform statistical analysis in SQL, the answer is ‘yes’. Read my article to learn how to do this! Statistics are very useful as an initial stage of a more in-depth analysis, i.e. for data overview and data quality assessment. However, SQL statistical analysis possibilities are somewhat limited as there are not many statistical functions in SQL Server.

Tag: Career in data science

Why Use SQL Over Excel

SQL is replacing Excel in many fields, and data analysis is certainly one of them. If you are still using Excel as a data analyst, you are missing something very valuable. SQL can make your life easier, as it's more efficient and faster than Excel. So, how and from where can you learn SQL? How Can SQL Help Data Analyst? You can use SQL to help you with the following work:

Career Change: From Accountant to Database Designer

How do career changes and life choices impact our future? Can we change the path that's been set for us? And if so, where do we begin? I wouldn't blame you if you thought this article is about change. In a sense, it is—it's in the title, after all. But for me, this article is more about what remains constant. If somebody were to ask me what hasn't changed for me since my childhood, I would know the answer immediately: curiosity.

Complete SQL Practice for Interviews

Congratulations! Your SQL skills were strong enough to get you that job interview! Now, if you only knew what SQL questions and practical exercises a recruiter might ask you to do… This article is meant as a SQL practice for interviews. I’ll help you prepare for the SQL and database aspects of your job interview. In a previous article, I explained how can you boost your career by learning SQL.

Finding the Perfect SQL Job

So you have some SQL skills and you're looking for a job that will use them. What are your options? SQL is everywhere, and there's a huge demand for people with database management skills. This is especially the case when companies start implementing Big Data solutions and strategies. There's no arguing that SQL is a must-have skill. If you're already proficient, how can you put your expertise to practical use in the job market?

A Day in the Life of a SQL Developer

What is a SQL developer? And what does a SQL developer do? Describing a “typical” day for a SQL developer is not easy. When your daily work is using various technologies to create interesting database-oriented products, very few days are alike! Each day brings a new and intriguing challenge. Nevertheless, I’ll have a go at explaining what everyday things a SQL developer might do. Morning: Arrive at Work What does a SQL developer do after arriving at the office?

Tag: Case

Useful SQL Patterns: Conditional Summarization with CASE

As you start coding in SQL, you will use some statements and techniques over and over again. We call these "SQL patterns". This series will look at the most common SQL patterns and consider how to use them. Previously, we looked at the SQL pattern of matching NULLs. This is important when you are comparing columns containing NULL values. Today, we're going to consider another SQL practice: conditional summarization with CASE operator.

Using CASE with Data Modifying Statements

What happens when you combine CASE with SQL's data modifying statements? Find out in this article. The CASE expression is a very useful part of SQL and one that you'll employ frequently. We've already covered what the CASE expression does, how to format it, and how to use it in a SELECT statement in "Using CASE to Add Logic to a SELECT". Another article, "How to Sort Records with the ORDER BY Clause"

Using CASE to Add Logic to a SELECT

As you write an SQL query, you may need to get values from multiple columns and change values from one form to another. The simple way to achieve this goal is to add a CASE expression to your SELECT statement. In this article, we'll introduce you to the syntax, formats, and uses of the CASE expression. The CASE expression is a conditional expression: it evaluates data and returns a result.

Tag: Cheat sheet

SQL Basics Cheat Sheet

Download this 2-page SQL Basics Cheat Sheet in PDF or PNG format, print it out, and stick to your desk. The SQL Basics Cheat Sheet provides you with the syntax of all basics clauses, shows you how to write different conditions, and has examples. You can download this cheat sheet as follows: Download 2-page SQL Basics Cheat Sheet in PDF format (A4) Download 2-page SQL Basics Cheat Sheet in PDF format (Letter) Download 1-page SQL Basics Cheat Sheet in PDF format (A3) Download 1-page SQL Basics Cheat Sheet in PDF format (Ledger) You may also read the contents here:

SQL JOIN Cheat Sheet

Download this 2-page SQL JOIN Cheat Sheet in PDF or PNG format, print it out, and stick to your desk. The SQL JOIN Cheat Sheet provides you with the syntax of different JOINs, and examples. You can download this cheat sheet as follows: Download 2-page SQL JOIN Cheat Sheet in PDF format (A4) Download 2-page SQL JOIN Cheat Sheet in PDF format (Letter) Download 1-page SQL JOIN Cheat Sheet in PDF format (A3) Download 1-page SQL JOIN Cheat Sheet in PDF format (Ledger) SQL JOINs Cheat Sheet JOINING TABLES JOIN combines data from two tables.

SQL Window Functions Cheat Sheet

Download this 2-page SQL Window Functions Cheat Sheet in PDF or PNG format, print it out, and stick to your desk. The SQL Window Functions Cheat Sheet provides you with the syntax of window functions, a list of window functions, and examples. You can download this cheat sheet as follows: Download 2-page SQL Window Functions Cheat Sheet in PDF format (A4) Download 2-page SQL Window Functions Cheat Sheet in PDF format (Letter) Download 1-page SQL Window Functions Cheat Sheet in PDF format (A3) Download 1-page SQL Window Functions Cheat Sheet in PDF format (Ledger) Window Functions Window functions compute their result based on a sliding window frame, a set of rows that are somehow related to the current row.

Tag: Common sql functions

18 Useful Important SQL Functions to Learn ASAP

Beginning with SQL: Useful Functions to Master Learning a new programming language can seem intimidating. Like any other language, a programming language has a large vocabulary that you need to master. In this article, we'll look at some of the most useful SQL functions that you need to know. There are many useful SQL functions for working with different data types. Once you practice with some of the most common ones, you'll gain enough confidence to move on to more advanced material.

Tag: Common sql mistakes

Extracting Data From a String: SPLIT_PART in PostgreSQL

Learn how to use split_part in PostgreSQL to extract data from strings. Quite often, we’d like to extract parts of a string when working with text values. A common example is when we have a full name and need to retrieve only the last name. In this article, we’ll examine how to do it using split_part in PostgreSQL, i.e. a string-related function that can be used to extract a substring.

How to Remove Junk Characters in SQL

Unwanted characters in text data can be a bit of a pain, but there’s an easy way to fix them. Scroll down to learn how to remove junk characters in SQL in the easiest way! Sometimes, we’ll find unwanted characters inside our string data because our SQL queries didn’t work as expected. Moreover, these extra characters may sometimes be invisible, which really complicates things. In this article, we’ll examine some string-related SQL functions that can handle unwanted characters—visible or not!

How to Solve Capitalization Data Quality Issues

Misspelled names, typos, and text data quality issues in your database? Power up your queries! Use SQL string functions to address data quality issues related to capitalization. Sometimes, our SQL queries don't work as expected because of data quality issues. In this article, we will examine some string-related SQL functions that can correct data quality issues related to capitalization. We'll be using PostgreSQL in our examples, but similar functions are available in most database engines.

Preventing Common SQL Mistakes

Regardless of the engine you are using (SQL Server, MySQL, Oracle, etc.), you can prevent common errors and simplify the debugging process. This article will discuss some of the common SQL mistakes you’ll face and will help you correct them easily. One of the best ways to prevent the most common SQL mistakes is to keep your queries clear and readable. It’s very easy to forget the ideas behind your code!

Tag: Common table expressions

How to Draw a Christmas Tree in SQL

You can use SQL to manipulate all kinds of data, from huge analytical queries to brief single-purpose statements. But you can also use SQL just for fun, without any business requirements stifling your creativity. So, get out your jolly hat and prepare to sing O Christmas Tree as we create some quirky art with plain old SQL. Today, we’re going to generate some holiday-themed ASCII art, just for fun. That’s right.

Simplify SQL Code: Recursive Queries in DBMS

Hey SQL users! Are you repeating the same query in every report? Are your queries getting too complicated? Use recursive queries to simplify SQL code! Too many SQL reports can lead to clutter on your desktop and in your head. And is it really necessary to code each of them separately? Ad-hoc queries can share much of the same SQL code with managerial reports and even regulatory reports. Suppose you’ve been writing basic SQL code for a while.

How to Organize SQL Queries with CTEs

Common table expressions (CTEs) allow you to structure and organize SQL queries. Knowing how to organize SQL queries is a necessity when you begin to move deeper into SQL, so if you want to become an SQL master, you need to know CTEs. The SQL CTE has been part of standard SQL for some time now. CTEs – which are also called WITH statements – are available in all major RDBMS.

Long SQL Query vs. Recursive SQL Query

Recursion is one of the central ideas in computer science. We can define it as a method for solving problems where the solution of the problem depends on solving a smaller instance of a problem. If this sounds complicated do not fret, in this article we will learn about recursion in SQL that you can practice and deepen in Vertabelo Academy. Recursion is a way of solving hierarchical problems we find in data with common SQL.

Tag: Conditional summarization

Useful SQL Patterns: Conditional Summarization with CASE

As you start coding in SQL, you will use some statements and techniques over and over again. We call these "SQL patterns". This series will look at the most common SQL patterns and consider how to use them. Previously, we looked at the SQL pattern of matching NULLs. This is important when you are comparing columns containing NULL values. Today, we're going to consider another SQL practice: conditional summarization with CASE operator.

Tag: Course of the month

SQL Course of the Month – SQL JOINs

If you want to really learn SQL, you can’t skip SQL JOINs. They are some of the most fundamental and commonly used features of the SQL language. That’s why SQL JOINs is our February SQL Course of the Month. What makes SQL JOINs so important? I asked Agnieszka Kozubek-Krycuń, Vertabelo's Chief Content Officer, about it. Here's what she said. Is it true that SQL JOINs are one of the foundations of SQL?

SQL Course of the Month – Standard SQL Functions

Are you dreaming of becoming a data analyst? Or maybe you just want to work effectively with your company’s databases? You can – with SQL functions. We’ve selected Standard SQL Functions to be our January 2021 SQL Course of the Month. What will you find inside? I asked Agnieszka Kozubek-Krycuń, Vertabelo's Chief Content Officer, about it. Here's what she said. What are SQL functions? The term reminds me of SELECT or JOIN.

SQL Course of the Month – Customer Behavior Analysis in SQL

Do you run a business? Do you want to squeeze even more out of your data? Start by analyzing your customers' behavior using SQL! Throughout December, you can learn how to do it for free on LearnSQL.com! I asked Agnieszka Kozubek-Krycuń, Vertabelo's Chief Content Officer, about our December Course of the Month, Customer Behavior Analysis in SQL. Here's what she told me. Let's start with the basics: Why analyze customer behavior?

SQL Course of the Month – GROUP BY Extensions in SQL

Do you want to develop your SQL skills? Do you want to get more out of your data and prepare better reports and summaries? The answer is learning to use SQL’s GROUP BY extensions. But how should you go about this? I asked the same question to Agnieszka Kozubek-Krycuń, Vertabelo’s Chief Content Officer. As she explains, the secret is in this November’s free SQL Course of the Month: GROUP BY Extensions in SQL.

SQL Course of the Month – How to INSERT, UPDATE, and DELETE Data in SQL

So, you've started learning SQL, and you already know what the SELECT command is and when to use it! Congratulations! Now, it's time to take the next step towards becoming an expert. You need to know the SQL UPDATE, INSERT, and DELETE commands to modify data in your tables. These are the basics that will allow you to work with tables. But what's the best way to learn them? I asked Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo.

SQL Course of the Month – Analyzing Revenue Trends in SQL

We work hard, we learn SQL, and we develop professionally. But why? For our own satisfaction, but also for money! The knowledge of SQL will increase your income significantly. If you are proficient in SQL, you can better analyze your company's revenue. How? I asked Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo. In this article, she answers your questions about our September SQL Course of the Month: Analyzing Revenue Trends in SQL.

SQL Course of the Month – Recursive Queries

Recursive Queries is one of SQL’s more advanced features. You could say they divide SQL users into beginners and experts. But how do you learn recursive queries? And why do you need them, anyway? Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo, is here to help. In this article, she answers your questions about our August SQL Course of the Month: Recursive Queries. Recursive queries … that sounds very serious.

SQL Course of the Month – PostGIS

It's summer, and it's travel time ... at least it would be under normal conditions. The pandemic is still going on, but that doesn't stop us from dreaming about distant trips and visits to beautiful places. For now, most of us will have to do it on a map. Did you know that databases can store geographical data? With interactive maps, if you find a nice summer house on the internet, you can accurately track it and plan the best route there.

SQL Course of the Month – SQL Practice Set

It is said that practice makes perfect. I agree with this statement one hundred percent. What is applicable in basketball training, playing an instrument, or learning a foreign language is also useful in learning SQL. Practicing writing queries, using functions, and putting together clauses is the basis for learning the true power of SQL. But how and where do you practice SQL? I spoke with Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo about this.

SQL Course of the Month – Creating Basic SQL Reports

In May, we chose Creating Basic SQL Reports as our course of the month. Why? Because the basis of every successful business is making the right decisions based on proven data and good SQL reports. I asked Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo, about this. She knows SQL better than just about anyone and is probably the best person to talk about SQL Reporting. What does it mean to create SQL reports?

SQL Course of the Month – Window Functions

Spring has come. It is nicer outside. It's a great time to learn something new. Which course should you choose? In April, it's worth it to bet on SQL window functions. What are they, what are they used for, and why are they worth knowing? I asked Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo, these questions. She has a PhD in mathematics and over 10 years’ experience teaching mathematics and computer science at the University of Warsaw.

Tag: Creating tables

Learn SQL Views in 30 Minutes

Views aren't complicated – if you've got half an hour, we'll get you started writing SQL queries using views! Let's start by answering the question "What is a view in SQL?'. A view is a database object (as is a table, an index, or a stored procedure). Like a table, you can query a view and extract the information in it. It can be used in the FROM clause of a SELECT, and you can reference view columns in clauses like SELECT, WHERE and GROUP BY among other clauses as well.

Tag: Cte

Where Can I Find Good SQL CTE Exercises?

Find the top online resources for SQL Common Table Expression (CTE) exercises! CTEs allow you to structure and organize SQL queries efficiently, which is essential if you want to advance your SQL knowledge. A Common Table Expression, or CTE, is a SQL syntax that creates a temporary data set. This set contains separate data than the main query, which can typically be referenced or reused in a subsequent query. A CTE is considered temporary because the result is not permanently stored anywhere and only exists for the duration of the query.

What’s the Difference Between SQL CTEs and Views?

SQL views vs. CTEs: What do they do? How are they different? Which one should you use and when? Get your answers here! In SQL, both CTEs (common table expressions) and views help organize your queries, leading to cleaner and easier-to-follow code. However, there are some important differences between them. This article will walk you through several examples of CTEs and views and explain when to use each one.

What are SQL CTE Best Practices?

Are you wondering what the best practices for using common table expressions are? This article will help you learn when to use a CTE and how to write it. If you have heard about SQL CTEs, you have probably noticed they’re often mentioned together with subqueries. Sometimes, people think there’s no difference compared to the subqueries, and there’s often debate about whether a CTE or subquery should be used to get a particular result.

How to Learn SQL Common Table Expressions (CTEs)

Common table expressions are very useful for organizing, traversing, and improving the readability of long SQL queries.  Moreover, recursive CTEs, which can reference themselves, solve problems that cannot be addressed with other queries. But how do you master common table expressions in SQL? In this article, I discuss the most effective strategies for learning CTEs and suggest how to address the common challenges of learning common table expressions on your own.

How to Use 2 CTEs in a Single SQL Query

Have you ever wondered how to use multiple CTEs in one SQL query? Read this article and find out about recursive CTEs. After learning common table expressions or CTEs, a natural question is “Can I use several CTEs in one query?” Yes, you can! And you can do it quite easily, especially if you already have some basic knowledge of CTEs. Whether you know a bit about CTEs or you’re entirely new to the CTE world, reading about what a CTE is is always a good start.

How CTEs Work

The SQL language offers a feature named Common Table Expressions, or CTEs. Also known as WITH clauses, CTEs are a fairly new addition to SQL. They help you break longer queries into smaller chunks, making your queries much easier to understand. Read the article to find out how to use CTEs and how they differ from traditional subqueries. Common Table Expressions (CTEs), which are essentially named subqueries, were first mentioned in the SQL standard between 1999 and 2000.

SQL CTEs Explained with Examples

Learn how you can leverage the power of Common Table Expressions (CTEs) to improve the organization and readability of your SQL queries. The commonly used abbreviation CTE stands for Common Table Expression. However, that simple fact doesn’t add much to your understanding. What does a CTE do? Why might you want to use one in your SQL code? Let’s answer those questions. What Is a CTE? A Common Table Expression is a named temporary result set.

When Should I Use a Common Table Expression (CTE)?

Interested in hearing more about common table expressions or CTEs? Would you like to know when CTEs are useful? Read on—we’ll discuss in this article. If you’ve heard of common table expressions, you’ve probably wondered what they do. Even if you have not, it’s good that you’re here! CTEs can be very useful, especially if you have already mastered the basics of SQL, such as selecting, ordering, filtering data, and joining tables.

What Is a CTE?

After mastering statements like SELECT, DELETE, INSERT, and GROUP BY, you might search for ways to improve code maintainability, reproducibility, and readability. At that point, you will probably start learning about modern SQL concepts that were introduced in the early 2000s. One such SQL technique is the CTE? (common table expression) —?a temporary named result set. In this article, you will learn what a CTE is and how to use it to improve the maintenance and the readability of your code.

How to Draw a Christmas Tree in SQL

You can use SQL to manipulate all kinds of data, from huge analytical queries to brief single-purpose statements. But you can also use SQL just for fun, without any business requirements stifling your creativity. So, get out your jolly hat and prepare to sing O Christmas Tree as we create some quirky art with plain old SQL. Today, we’re going to generate some holiday-themed ASCII art, just for fun. That’s right.

Simplify SQL Code: Recursive Queries in DBMS

Hey SQL users! Are you repeating the same query in every report? Are your queries getting too complicated? Use recursive queries to simplify SQL code! Too many SQL reports can lead to clutter on your desktop and in your head. And is it really necessary to code each of them separately? Ad-hoc queries can share much of the same SQL code with managerial reports and even regulatory reports. Suppose you’ve been writing basic SQL code for a while.

How to Organize SQL Queries with CTEs

Common table expressions (CTEs) allow you to structure and organize SQL queries. Knowing how to organize SQL queries is a necessity when you begin to move deeper into SQL, so if you want to become an SQL master, you need to know CTEs. The SQL CTE has been part of standard SQL for some time now. CTEs – which are also called WITH statements – are available in all major RDBMS.

Long SQL Query vs. Recursive SQL Query

Recursion is one of the central ideas in computer science. We can define it as a method for solving problems where the solution of the problem depends on solving a smaller instance of a problem. If this sounds complicated do not fret, in this article we will learn about recursion in SQL that you can practice and deepen in Vertabelo Academy. Recursion is a way of solving hierarchical problems we find in data with common SQL.

How Recursive Common Table Expressions Work

Recursive Common Table Expressions are immensely useful when you're querying hierarchical data. Let's explore what makes them work. Common Table Expressions (CTEs) are some of the most useful constructions in SQL. Their main purpose is improving query design, which makes queries easier to read. One of the reasons CTEs are so popular is that they let you divide longer queries into shorter subqueries. These are easier to read and edit.

How to Organize SQL Queries When They Get Long

The first long SQL query you’ll have to deal with is likely to be hard for you to structure and understand. These five tips will teach you the best way to organize SQL queries, i.e. write and format them. As we all know, SQL queries are essential to database management. Without them, it would be extremely difficult to find and work with the information in a database. Query length depends on the type of information we need and the size of the database.

Improving Query Readability with Common Table Expressions

What is a Common Table Expression, or CTE? Where do you use them, and why? This post answers your questions. Simply put, Common Table Expressions (also known as WITH clauses) are essentially named subqueries. They also provide additional features like recursion. If you're new to subqueries, I recommend you read the SQL Subqueries article before continuing. The main purpose of Common Table Expressions is to improve the design and readability of an SQL statement.

Tag: Data analysis

6 Advanced SQL Queries for Analyzing Financial Data

Are you an advanced SQL user who’s new to finance? Do you want to learn how to use your knowledge to analyze financial data? The article will give you some guidance. You probably know that SQL is a potent tool for analyzing all sorts of data. The bigger and more complex data, the more beneficial SQL becomes. In certain situations, financial data can be very complicated; producing a sophisticated analysis requires sophisticated tools.

Why Use SQL Over Excel

SQL is replacing Excel in many fields, and data analysis is certainly one of them. If you are still using Excel as a data analyst, you are missing something very valuable. SQL can make your life easier, as it's more efficient and faster than Excel. So, how and from where can you learn SQL? How Can SQL Help Data Analyst? You can use SQL to help you with the following work:

SQL Indexing 101

Indexes are one of the most misused and misunderstood entities in physical database design. A good understanding of indexes and how they solve database performance problems is necessary for any database novice. In this article, we'll look at basic database indexes and their role in database development. To picture what an index is, consider a textbook. At the end of most textbooks is an index listing all the terms one can find in the text and the pages on which they appear.

How to Use a SQL Wildcard

SQL wildcard allows us to filter data matching certain patterns in SQL. We use SQL wildcards with the LIKE operator in the WHERE clause of a query to filter data. In this beginner’s article, we’ll look at everything you need to know about basic SQL wildcards. If you like playing cards, then you know that wildcards can substitute any other card in your deck. Similarly, SQL wildcards can substitute one or more characters.

Our Picks for 2020’s 7 Best Online SQL Schools

If you’re looking for the best online SQL courses but aren’t sure where to start, you’re in the right place. I evaluated the top 7 ranked SQL schools available online to help you find the right solution. While summer is a great time to relax and get away from work, it’s also an excellent opportunity to learn new skills – like SQL! Thanks to SQL schools putting their courses on the internet, learning new tech skills is super easy and you can choose from a variety of formats to suit your needs.

Why Learn SQL Over the Summer

Think summer is reserved for flying to warm places and hanging out at the beach? Sure! But it's also a great time to learn new skills that you haven't had time for. If you recently graduated from high school and want to get a head start on computer programming for college, learning SQL over the summer is a great opportunity. You have nothing to lose and everything to gain—SQL is actually really easy to learn, especially with so much free time over the summer.

Key Insights for Mastering SQL Queries Using Tinder Data Example

Going from zero to one can be daunting in any endeavor. The same is true for learning new programming languages, even simple ones like SQL. In this article, we’ll take a look at some key insights that will help you understand the nuances of mastering SQL queries. If you’ve never used SQL, you’re in the right place. When learning anything new, you’ll find that there are always some key insights or tips that can help you on your way.

Improving Slow Query Performance: When Runtime Matters

As SQL users, we usually focus on writing queries that return correct results. However, there are more things to consider when you're writing a query; one of them is query performance. In this article, we'll look at some examples where query response time is critical. Scene One: 911 Call Center Let's suppose we're at a 911 call center, when the phone rings. One of the operators answers the call; a witness reports that a man has been shot.

Converting Subqueries to Joins

Not all queries are alike, especially in terms of performance. In this article, we'll look at how you can convert SQL subqueries to joins for improved efficiency. When should I use SQL subqueries? Great question! Unfortunately, there's no concrete answer. SQL beginners tend to overuse subqueries. Typically, once they find that SQL construction works in one situation, they try to apply that same approach to other situations. It's only natural.

Learn to Write a SQL Correlated Subquery in 5 Minutes

If you’re familiar with the famous Russian nesting doll, then SQL correlated subqueries should be a peace of cake to understand—subqueries are just queries nested within queries. An SQL subquery is often called an “inner” query; the main query is usually called the “outer” query. This article covers everything you need to know about correlated subqueries. What Exactly is a SQL Correlated Subquery? A correlated SQL subquery is just a subquery that is executed many times—once for each record (row) returned by the outer (main) query.

How to Become a Database Analyst

Curious about becoming a database analyst? Maybe you've taken some database courses at university and they really struck a chord. Or maybe you learned online. Now you're thinking about making a career out of working with databases. Where would you start? What should you expect at each phase of your professional development? In this post, we'll explore the challenging and exciting world of databases analysis. We'll go from the very beginning of a career to the apex of professional success.

Extracting Data From a String: SPLIT_PART in PostgreSQL

Learn how to use split_part in PostgreSQL to extract data from strings. Quite often, we’d like to extract parts of a string when working with text values. A common example is when we have a full name and need to retrieve only the last name. In this article, we’ll examine how to do it using split_part in PostgreSQL, i.e. a string-related function that can be used to extract a substring.

High-Performance Statistical Queries: Dependencies Between Discrete Variables

In my previous article, we looked at how you can calculate linear dependencies between two continuous variables with covariance and correlation. Both methods use the means of the two variables in their calculations. However, mean values and other population moments make no sense for categorical (nominal) variables. For instance, if you denote "Clerical" as 1 and "Professional" as 2 for an occupation variable, what does the average of 1.5 signify?

Digging Into Data: Explore and Analyze Survey Results With SQL

Excel is a powerful beast that lets you analyze complex data. Yet, operating on big chunks of data can sometimes be a daunting task. Let's take a look at how SQL can help. Today, we'll tackle a common problem with importing data to an SQL database, using a real-life example. Suppose your company conducted a survey on the most popular programming trends and preferences, striving to meet the expectations of its users.

SQL Hacks To Control Family Budget On Black Friday Weekend

If you’re in the US, chances are you’ve been eagerly awaiting the approach of Black Friday just as much as Thanksgiving. Though the shopping frenzy takes hold of nearly everyone, some people have to stick to their budgets and shop prudently. In this article, we’ll take a look at how generating an SQL report can help you track how much your family spent shopping on Black Friday. Storing Black Friday Purchases in a Database Before we can create an SQL report, we first need some data we can use.

Introduction to Reporting with SQL — the Ultimate Tutorial for Business Professionals

Working with the financial aspects of large and small enterprises can be a daunting task for a business professional. In this article, we'll look at several ways of constructing the perfect SQL report. You've probably already heard about SQL from your colleagues or in other areas of your career. If you're here, you've likely concluded that learning SQL will make your professional life easier – and you're right!

SQL Statistical Analysis Part 1: Calculating Frequencies and Histograms

Database and Business Intelligence (BI) developers create huge numbers of reports on a daily basis, and data analyses are an integral part of them. If you wonder whether you can perform statistical analysis in SQL, the answer is ‘yes’. Read my article to learn how to do this! Statistics are very useful as an initial stage of a more in-depth analysis, i.e. for data overview and data quality assessment. However, SQL statistical analysis possibilities are somewhat limited as there are not many statistical functions in SQL Server.

Tag: Data analyst

Google Analytics and SQL

Google Analytics is a very popular tool among website and blog owners alike. With a simple and quick setup, it lets you gather data about your web page visitors easily. However, did you know that you can export data from Google Analytics to create your own SQL reports? Read this article to find out how. Google Analytics is an extremely popular and powerful solution that lets you collect and analyze various kinds of information about your website.

Should I Learn SQL as a Data Analyst?

So, you are a data analyst—someone who relies on data. You like to gather, clean, and transform data and come to conclusions based on data. You are a data detective. Which tool do you choose to do your job in an elegant, reproducible, and simple way? Excel? R? Python? Or should you learn SQL? Stay tuned! In this article, I will explain why SQL is a must-have skill for data analysts.

SQL Statistical Analysis Part 1: Calculating Frequencies and Histograms

Database and Business Intelligence (BI) developers create huge numbers of reports on a daily basis, and data analyses are an integral part of them. If you wonder whether you can perform statistical analysis in SQL, the answer is ‘yes’. Read my article to learn how to do this! Statistics are very useful as an initial stage of a more in-depth analysis, i.e. for data overview and data quality assessment. However, SQL statistical analysis possibilities are somewhat limited as there are not many statistical functions in SQL Server.

Tag: Data driven organization

How SQL supports data-driven organization

Typical business users make decisions based on gut feelings, but this can't get them so far. In this article, we'll look at how learning to write basic SQL queries helps your company become a data-driven organization. Businesses face many decisions. Do we increase our advertising budget in one region or the other? Are certain products selling quickly enough? What we should do if they aren't? Most of these decisions are driven by intuition, but organizations that make the most business impact use data-driven decision-making.

Tag: Data engineering

What Is a Unique Constraint in SQL?

To ensure the uniqueness of data in a database, we use the SQL UNIQUE constraint. In this article, we’ll discuss how, when, and why to implement it. The idea of a unique constraint is not unique to SQL; it’s a familiar concept in real life, although we probably call it something else! For example, think of ID numbers. There can be only one social security number (SSN) per person and each one must be unique.

Data Types in SQL

Read this article and learn the ABC of SQL data types. Data types are used to define the type of data stored in a database. However, there are related concepts that a good SQL developer should know: data type conversion, what operations are possible between different data types, date arithmetic, etc. SQL also provides functions that manipulate values of different data types (i.e. functions for string data, date and time data, etc.

What Is Auto-Increment in SQL?

In this article, we’ll learn the basics of the auto-increment feature of SQL: what it is and how to use it efficiently. One of the many features offered by SQL is auto-increment. It allows us to automatically generate values in a numeric column upon row insertion. You could think of it as an automatically supplied default value – the next number in a number sequence – that’s generated when the row is inserted.

LearnSQL Track of the Season: Creating Database Structure

New year, new challenges, and ... a new SQL Track of the Season! Start 2021 by learning SQL and data engineering. In this article, we answer frequently asked questions about our Creating Database Structure track. Maybe you haven't noticed yet that there’s an order to many LearnSQL.com courses; you can learn SQL by doing them in the right order. We call this option our ‘SQL tracks’. These are logically structured and well-thought-out learning paths that will help you take the next steps towards becoming an SQL expert.

What is an SQL View?

A view is a well-known feature in SQL. It allows you to create a virtual table based on an SQL query referring to other tables in the database. A view stores an SQL query that is executed whenever you refer to the view. This is a convenient way to get the desired data because it is easier to run a query stored in a view than to type a query from scratch.

What Is a Foreign Key in SQL?

What does a foreign key do in SQL? Why would you need one? Learn the ABCs of foreign keys in five minutes. Foreign keys are a central concept in SQL databases; they allow us to enforce data consistency. Usually they work with primary keys to connect two database tables, like a virtual bridge. All SQL developers need to know what SQL foreign keys are, how they work, what data values are allowed in them, and how they’re created.

What Is a SQL Constraint?

What are SQL constraints? When and why should you use them? We give examples of common constraints and demonstrate how to apply them. When you’re creating a relational database, you often want to impose certain restrictions on some columns. For example, a column containing a social security number should store only unique values; a column containing a date of birth should not be null, or left empty. These conditions can be ensured by using SQL constraints.

Top 7 Online Courses for Data Engineers

This article summarizes the top online courses available for data engineers. We have picks suitable for beginners as well as intermediate learners. If you’re interested in database design and management, check these courses out! Most individuals who aspire to enter the realm of data aim for data scientist or data analyst roles. While these roles are indeed very rewarding because of their tangible links to customers and business direction, the role of data engineers is equally vital for businesses that operate in a data-rich environment.

What is a Primary Key in SQL?

Primary keys are an important concept in SQL databases. They provide a unique ID for every row in a database table. As an SQL developer, you should know what primary keys are, what data values are allowed in them, and how to create them. Read this article to learn the ABCs of primary keys in 10 minutes. How to Identify Rows in a Table Tables are the main objects in an SQL database, and as you probably know, tables store records or rows.

What Is a DBMS?

We generate vast quantities every day, and that data needs to be stored somehow. That’s where DBMSs come in handy. Find out what they are and how they relate to databases. If you go on a diet and simply want to keep track of your weight, you can probably use a piece of paper and a pencil. If you then want to chart your daily caloric intake, you’ll probably switch to something like a computer spreadsheet.

How to Create Your First Table in SQL

Creating a database table with SQL is one of the core skills you’ll need to work with data. And it’s easy to learn, so let’s get started! Imagine you’re analyzing data and want to store your results in a database table. Sure, you've done this a million times in Excel. But you’re not sure how to create a table with SQL. Or maybe you’ve noticed that data engineering is in high demand and you want to start learning its core concepts.

How Much Do Data Engineers Earn in 2020?

Data engineering is a hot job right now. What does a data engineer do? And just how much do they earn? We’ve done the research for you. If you are reading this, you’re either starting to learn SQL or you already know some and feel it’s time to look around for a SQL job. Maybe you’re in the midst of tackling our Creating Database Structure track. And, let’s be honest, maybe you need some extra motivation to keep on you track.

How to Create a Table in SQL

Creating tables in databases is a very helpful skill, and not just for software engineers or database administrators. It allows you to design or change the structure of a database and store data that’s related to each other. In this article, you’ll learn what a database table is, who creates them, and how to use the syntax of the CREATE TABLE command. What Is a Database Table? A relational database is built of various structures like tables, views, procedures, and triggers.

Who Is a Data Engineer?

A new kind of job has recently emerged in the IT world: Data Engineer. At first sight, it may seem very similar to Data Analyst or Data Scientist positions. However, our article explains all the important differences. We present the skills, tools, and everyday tasks of Data Engineers. We also explain how you can get started with this career path.   Thirty years ago, we typically used terms such as “Computer Scientist” when referring to anyone working with computers.

LearnSQL.com’s New Learning Path: Data Engineering

Calling all future data engineers! Would you like to learn to use SQL? Then our new Data Engineering Learning Path is just for you! We’re very excited to announce the release of a new learning path at LearnSQL.com: Data Engineering, published in July 2020. This is the second learning path offered in our platform. So far, we offered an analytical path, SQL Querying & Reporting, that focuses on writing queries and business reports in SQL.

What Is Data Engineering?

Data Engineering is a fairly new term in IT. And it’s getting more and more attention. You may have heard about a few similar fields like data science, Big Data, and machine learning. This article explains the difference between these concepts and shows how they can be combined to analyze vast amounts of data. When computers first appeared, their storage capacity was very limited. Do you remember floppy disks? They were popular in the late 20th century and typically offered around 1.

TRUNCATE TABLE vs. DELETE vs. DROP TABLE: Removing Tables and Data in SQL

What’s the difference between truncating, deleting, and dropping a table in SQL? Find out in this article. There are a lot of ways to delete data in SQL, including the DELETE, TRUNCATE TABLE and DROP TABLE commands. Which one should you use in a given situation? In this article, you’ll learn the syntax of each command in different database engines like MySQL, PostgreSQL, SQL Server, and Oracle. And you’ll understand the DROP TABLE vs.

Tag: Data modifying

Simplify SQL Code: Recursive Queries in DBMS

Hey SQL users! Are you repeating the same query in every report? Are your queries getting too complicated? Use recursive queries to simplify SQL code! Too many SQL reports can lead to clutter on your desktop and in your head. And is it really necessary to code each of them separately? Ad-hoc queries can share much of the same SQL code with managerial reports and even regulatory reports. Suppose you’ve been writing basic SQL code for a while.

Using CASE with Data Modifying Statements

What happens when you combine CASE with SQL's data modifying statements? Find out in this article. The CASE expression is a very useful part of SQL and one that you'll employ frequently. We've already covered what the CASE expression does, how to format it, and how to use it in a SELECT statement in "Using CASE to Add Logic to a SELECT". Another article, "How to Sort Records with the ORDER BY Clause"

Tag: Data quality

Extracting Data From a String: SPLIT_PART in PostgreSQL

Learn how to use split_part in PostgreSQL to extract data from strings. Quite often, we’d like to extract parts of a string when working with text values. A common example is when we have a full name and need to retrieve only the last name. In this article, we’ll examine how to do it using split_part in PostgreSQL, i.e. a string-related function that can be used to extract a substring.

How to Remove Junk Characters in SQL

Unwanted characters in text data can be a bit of a pain, but there’s an easy way to fix them. Scroll down to learn how to remove junk characters in SQL in the easiest way! Sometimes, we’ll find unwanted characters inside our string data because our SQL queries didn’t work as expected. Moreover, these extra characters may sometimes be invisible, which really complicates things. In this article, we’ll examine some string-related SQL functions that can handle unwanted characters—visible or not!

How to Solve Capitalization Data Quality Issues

Misspelled names, typos, and text data quality issues in your database? Power up your queries! Use SQL string functions to address data quality issues related to capitalization. Sometimes, our SQL queries don't work as expected because of data quality issues. In this article, we will examine some string-related SQL functions that can correct data quality issues related to capitalization. We'll be using PostgreSQL in our examples, but similar functions are available in most database engines.

Tag: Data types

Understanding Numerical Data Types in SQL

Working with databases of any kind means working with data. This data can take a couple of predefined formats. As you start on your learning path with LearnSQL.com, you will start to understand SQL's different data types. In this article, we will cover different variations of the SQL numeric data type. We'll also examine some functions that convert data from one type to another. Creating tables is the first step in any SQL coding project.

How to Recognize SQL Text Data Type

How can you store textual information in database tables? Thanks to this post, you’ll learn the characteristics of every text data type in SQL Note: This post is intended for readers familiar with SQL data definition language (DDL) and the DDL CREATE statement. To learn more about DDL, check out LearnSQL.com. Most data types are classified as NUMERIC, CHARACTER, or DATE. In this post, we’re going to focus on each CHARACTER or text data type in SQL.

Tag: Date and time

Useful SQL Patterns: Date Generator

As you start coding in SQL, you will use some statements and techniques over and over again. We call these “SQL patterns”. This series will look at the most common SQL patterns and consider how to use them. SQL patterns, such as the pivot pattern we discussed last week, can save you a lot of time and effort. Suppose you are asked to get a range of days in a financial quarter, but the only records you have are for the start and end dates of each quarter.

Performing Calculations on Date- and Time-Related Values

Relational databases support several date and time data types. In this article, we'll look at several arithmetic operations we can do on these types. These operations are logical and understandable, even for the beginning SQL coder. Let's first briefly explain the main data types used for dates and times. Keep in mind that data types may differ by database engine, so check your database documentation for specifics before you start working with them.

The Most Useful Date and Time Functions

Date and time functions and formats are quite different in various databases. In this article, let's review the most common functions that manipulates dates in an Oracle database. The function SYSDATE() returns a 7 byte binary data element whose bytes represents: century, year, month, day, hour, minute, second It's important to know that select sysdate from dual in SQL*Plus gives the same result as select to_char(sysdate) from dual because SQL*Plus binds everything into character strings so it can print it.

Tag: Date arithmetic

The SQL Coalesce Function: Handling Null Values

You may already know how to return null values in SQL. Now, we’re going to learn how to do the opposite. Though the SQL COALESCE function may seem complex, it’s actually very straightforward and useful. Let’s look at several examples of how the SQL COALESCE function can be used to work with NULL values in SQL. The Need for Coalesce in SQL Before we dive into the SQL COALESCE function in detail, you should understand how NULL values behave in expressions.

How Often Employees Are Running Late for Work: SQL Datetime and Interval SQL Arithmetic

Computing Tardiness: Date, Time, and Interval SQL Arithmetic In this article, we’re going to discuss some interesting operations we can perform with date-related data types in SQL. The SQL standard, which most relational databases comply with these days, specifies the date-related data types that must be present in relational databases. The most important of such data types are date, time, timestamp, and interval. Here’s a brief rundown of the differences between these data types:

Tag: Date functions

18 Useful Important SQL Functions to Learn ASAP

Beginning with SQL: Useful Functions to Master Learning a new programming language can seem intimidating. Like any other language, a programming language has a large vocabulary that you need to master. In this article, we'll look at some of the most useful SQL functions that you need to know. There are many useful SQL functions for working with different data types. Once you practice with some of the most common ones, you'll gain enough confidence to move on to more advanced material.

Tag: Delete

Learn SQL Views in 30 Minutes

Views aren't complicated – if you've got half an hour, we'll get you started writing SQL queries using views! Let's start by answering the question "What is a view in SQL?'. A view is a database object (as is a table, an index, or a stored procedure). Like a table, you can query a view and extract the information in it. It can be used in the FROM clause of a SELECT, and you can reference view columns in clauses like SELECT, WHERE and GROUP BY among other clauses as well.

Using CASE with Data Modifying Statements

What happens when you combine CASE with SQL's data modifying statements? Find out in this article. The CASE expression is a very useful part of SQL and one that you'll employ frequently. We've already covered what the CASE expression does, how to format it, and how to use it in a SELECT statement in "Using CASE to Add Logic to a SELECT". Another article, "How to Sort Records with the ORDER BY Clause"

Tag: Duplication

How to Track Down Duplicate Values in a Table

When it comes to information management, duplicates present one of the most common challenges to data quality. In this article, I'll explain how it is possible to find and distinguish duplicate names with the help of the SQL data programming language. I really like my maiden name. The reason I like it so much is because it's rare. My maiden name (first with last) provided a unique identifier on platforms such as LinkedIn, Facebook, Twitter and similar.

Tag: E learning

How to Practice SQL with LearnSQL.com

Practicing new skills online needs motivation and self-discipline, but it’s worth it. We’re facing a difficult, uncertain time. On one hand, the COVID pandemic caused a lot of fear. What will happen in the future? Will I keep my job? Will we stay safe and healthy? On the other hand, COVID is giving us a lot of time. Working remotely, not having anything to do but stay home and… And what?

Top 5 Beginner Online SQL Courses in 2020

Looking for an exciting new career? Data analysis won’t disappoint you! The simplest way to make this possible is by learning SQL, and online SQL courses are the most effective learning method. Don’t know where to start? Here’s an overview of the best online SQL courses for complete beginners. There are infinite reasons for changing your industry. You may want to land a new job because you’re burnt out. You may be bored and want something more challenging.

Choose the Best Way to Learn SQL

SQL has become a hot topic in the professional world, and many resources have appeared both online and offline for learning SQL. It’s easy to get lost in the jungle of books, tutorials, and courses. Which resources do you choose? If you want to know how to learn SQL quickly and effectively, take a look at my list. There are many reasons for learning SQL. We asked our users about them and learned that there was no universal motive.

Online Education in the Times of COVID-19

LearnSQL.com grants free access to their Interactive courses till 04/20/2020. People around the world are faced with a new challenge. A challenge which requires swift action and adaptability. Students and teachers, employers and employees, families and friends. Many have shown vigilance and decisiveness, while at the same time trying their best to maintain their everyday-life continuity. However, there are those who, due to the current circumstances, need to postpone plans and invest their resources in different areas.

Stay at Home and Learn SQL for Free with LearnSQL.com

Working remotely is a dream come true for some. You ditch commuting and have more time for the people you love and the things you enjoy. For others, it's a challenge to maintain their focus when there are new distractions. It's also an opportunity to invest the few gained hours in learning something new. Staying at home can be a time when you might find yourself busier than you've ever been, but not getting many things done, and worse, not learning what you planned to.

What Programming Language Should You Learn?

If you've ever been wondering which programming language you should learn first, you know that's a tough nut to crack. It’s especially difficult if you are new to IT and programming. In this article, I give suggestions for what to learn first and what perspectives each language can give you in IT. There are hundreds of programming languages, and new ones are showing up all the time. Getting to know all of them is simply impractical and impossible.

How to Study Online: 5 Steps to Becoming an Effective Learner

If you suffer from procrastination or lack of motivation, you’re not alone. We have some online learning tips to make your learning journey smoother and more enjoyable. One of the best things about being an adult is that we can do what we want: go to sleep late at night, party until morning, eat junk food. Besides all those small pleasures, as adults we are responsible for ourselves, our choices, and our mistakes.

Tag: Elearning

A Non-Technical Introduction to Learning SQL on Your Lunch Break

Do you think learning SQL will help you in your career? You are right. SQL is one of the easiest computer languages to learn. These days many non-IT employees have SQL skills and use them to extend their professional capacity. Moreover, more and more companies are encouraging their employees in non-IT areas (like sales, advertising, and finances) to learn and use SQL. One of the benefits of empowering employees with SQL skills is that once you answer one data question, the results will generate a new data question, and then perhaps a cascade of further data questions.

SQL Mythbuster – 5 Reasons Why No One Should Be Afraid of SQL

Anyone can learn SQL. It’s not as hard as you think! In today’s world, even those in non-technical jobs need some technical skills. And you don’t have to be a hard-core nerd to get these skills. Let me tell you my own story. A few years ago, I wasn’t considering learning SQL or anything else that I labelled “technical”. My background is in sociology, journalism, and scriptwriting, and I thought computer languages were pretty sci-fi.

How to Learn SQL: 6 Ideas for Newbies

Learning a new skill can be a daunting task, especially in programming. SQL is not immune to this. Luckily, with the Internet and the explosion of programming-related information out there, there are a lot of options you can use to undergo your SQL training! But we then come to a new roadblock. Where to begin? How will we know which option is best for our budget, skill level, and schedule?

Tag: Extras

SQL INSERT, SQL UPDATE, SQL DELETE – Oh My!

Need to understand SQL INSERT, UPDATE, or DELETE? We'll get you up to speed with a comprehensive How-To and useful examples! SQL INSERT, UPDATE, and DELETE statements—what are they all about? If you're a data engineer, a database administrator, or even just your average data fanboy or girl, one day you're going to find yourself with a database that becomes your "baby." Charged with this special bundle of joy, you're going to need to feed and change the little fella.

SQL, Databases, and Hollywood Movies

Policemen, doctors, lawyers, scientists, teachers: These are the professions that we often see in Hollywood movies. But are movies also trying to show what the work of data analysts looks like? Here is a list of six movies in which screenwriters, directors, and producers decided to cast SQL and databases in the main roles. Data analysis is most often associated with business, reporting, and making key decisions for the company.

Career Change: From Accountant to Database Designer

How do career changes and life choices impact our future? Can we change the path that's been set for us? And if so, where do we begin? I wouldn't blame you if you thought this article is about change. In a sense, it is—it's in the title, after all. But for me, this article is more about what remains constant. If somebody were to ask me what hasn't changed for me since my childhood, I would know the answer immediately: curiosity.

Forget About Excel, High Five With SQL

Find out why you should forget about Excel and start using SQL even if you're not an IT expert. We'll show you how easy it is to learn SQL, how it can make you work better, and how LearnSQL.com makes the learning process fun. "I Don't Deal With Data" We frequently hear the sentence above from people outside the IT industry. Well, it's not entirely true. Data is now almost everywhere.

How to Install PostgreSQL on Windows 10 in 5 Minutes

It may look like a complicated task to install PostgreSQL, Oracle, or SQL Server or any other database software, but it really isn’t! These days, most relational database management systems come with installation wizards that make the process much simpler. In this article, we’ll look at how to install PostgreSQL and test that the installation is working. Install PostgreSQL: Steps Involved To install PostgreSQL, we’ll complete the following tasks:

Our Picks for 2020’s 7 Best Online SQL Schools

If you’re looking for the best online SQL courses but aren’t sure where to start, you’re in the right place. I evaluated the top 7 ranked SQL schools available online to help you find the right solution. While summer is a great time to relax and get away from work, it’s also an excellent opportunity to learn new skills – like SQL! Thanks to SQL schools putting their courses on the internet, learning new tech skills is super easy and you can choose from a variety of formats to suit your needs.

Why Learn SQL Over the Summer

Think summer is reserved for flying to warm places and hanging out at the beach? Sure! But it's also a great time to learn new skills that you haven't had time for. If you recently graduated from high school and want to get a head start on computer programming for college, learning SQL over the summer is a great opportunity. You have nothing to lose and everything to gain—SQL is actually really easy to learn, especially with so much free time over the summer.

Essential SQL Terms to Know for Beginners and Pros

Working with databases can seem daunting to a non-technical person. Right away, you’re bombarded with new terms that make your head spin. Database, database instance, table, SQL and others are some of the basic terms that you need to understand just to have a normal conversation with your technical colleagues. In this article, we’ll explore some basic SQL database terminology you need to know to succeed. Imagine you’re attending a meeting with the development staff and suddenly feel as if you’re listening to white noise.

15 Best SQL Articles for Beginners Published in 2017

For this post, I've gathered 15 of the most interesting SQL articles published in 2017. If you're looking for articles on SQL for beginners, want to learn more about databases and SQL queries, or just expand your knowledge of SQL, this article is perfect for you. Let's dive right in! Top 3 Vertabelo Academy Articles I'll start off the list with three of the most popular Vertabelo Academy SQL articles.

How to Draw a Christmas Tree in SQL

You can use SQL to manipulate all kinds of data, from huge analytical queries to brief single-purpose statements. But you can also use SQL just for fun, without any business requirements stifling your creativity. So, get out your jolly hat and prepare to sing O Christmas Tree as we create some quirky art with plain old SQL. Today, we’re going to generate some holiday-themed ASCII art, just for fun. That’s right.

SQL Hacks To Control Family Budget On Black Friday Weekend

If you’re in the US, chances are you’ve been eagerly awaiting the approach of Black Friday just as much as Thanksgiving. Though the shopping frenzy takes hold of nearly everyone, some people have to stick to their budgets and shop prudently. In this article, we’ll take a look at how generating an SQL report can help you track how much your family spent shopping on Black Friday. Storing Black Friday Purchases in a Database Before we can create an SQL report, we first need some data we can use.

What Is Vertabelo’s SQL Cheat Sheet?

Everyone, from rookie programmers to SQL ninjas, needs a bit of help now and again. Enter Vertabelo's SQL Cheat Sheet! Working with databases is hard. There's a lot of data to manage, which can be daunting. But the main challenge many database users face is the SQL commands themselves. It's all right when you're using the same familiar ones day after day, but what about the commands you dust off once or twice a year?

The 5 Highest Paying Jobs That Use SQL

IT provides a wide and growing job market, offering many excellent opportunities in both career development and earning potential. Today we’ll take a look at several very interesting types of database jobs that use SQL. Every year, many in the work force set their sights and aim for new and better jobs. When it comes to jobs, “better” means different things to different people, but earning potential is almost always a top priority.

SQL Mythbuster – 5 Reasons Why No One Should Be Afraid of SQL

Anyone can learn SQL. It’s not as hard as you think! In today’s world, even those in non-technical jobs need some technical skills. And you don’t have to be a hard-core nerd to get these skills. Let me tell you my own story. A few years ago, I wasn’t considering learning SQL or anything else that I labelled “technical”. My background is in sociology, journalism, and scriptwriting, and I thought computer languages were pretty sci-fi.

5 Books That Will Grow Your SQL Skills

Which books will help you build your database skills? We look at five awesome SQL books. There’s a common saying that “all wise men read books”. I would say that all professionals read books – particularly those related to their field. There are many books about databases and SQL; most are tied to specific vendors (DB2, Oracle, MS SQL) but there are also plenty that are vendor-neutral. In this article, I’m going to review a few books that I would recommend to SQL learners at various levels of proficiency.

Should I Learn SQL? 4 Convincing Reasons

There are 250+ computer programming languages in popular use. Why should you learn SQL, or Structured Query Language? Why Should You Learn SQL? Why learn SQL? To answer this question, you should start with reflecting on your professional life. Are you interested in boosting your career? Wondering what skills are worth investing in? If you’re currently in your dream job, still searching for it, or even thinking about starting your own business, it pays to develop your technical skills.

Tag: Fetch

Oracle Top-N Queries for Absolute Beginners

It's common to run a query using only part of a dataset – for example, the top 100 salespeople in a company. In this article, we'll see how to use Oracle's Top-N query method to query just these rows. Top-N queries retrieve a defined number of rows (top or bottom) from a result set. In other words, they find the best or worst of something – the ten best selling cars in a certain region, the five most popular routers, the 20 worst-performing stores, etc.

Tag: Foreign key

Referential Constraints and Foreign Keys in MySQL

Foreign keys and referential constraints allow you to set relationships between tables and modify some of the database engine’s actions. This beginner’s guide explains referential integrity and foreign key use in MySQL. One of the most important aspects of database usage is being able to trust the information you store. Database engines provide several features that help you maintain the quality of your data, like defining required columns as NOT NULL and setting an exact data type for each column.

Tag: Free sql course

Stay at Home and Learn SQL for Free with LearnSQL.com

Working remotely is a dream come true for some. You ditch commuting and have more time for the people you love and the things you enjoy. For others, it's a challenge to maintain their focus when there are new distractions. It's also an opportunity to invest the few gained hours in learning something new. Staying at home can be a time when you might find yourself busier than you've ever been, but not getting many things done, and worse, not learning what you planned to.

Tag: Functions for manipulating sql strings

5 SQL Functions for Manipulating Strings

SQL functions used for manipulating strings, commonly called string functions, are among most important SQL’s tools. In this post, we’ll look at five ways you can perform various operations on strings. There are many SQL functions that let you “edit” string data. As you learn SQL, you’ll see how useful they prove. Some sql trim off unneeded spaces or characters; others tell you how long a string is. These functions give you a lot of opportunities to transform and work with strings, which makes your code more effective.

Tag: Game

Can SQL Help Solve Crossword Puzzles?

Everyone has solved crossword puzzles and has certainly had some problems finding an appropriate word. Thanks to SQL, it is ridiculously simple to quickly dispel your crossword doubts and give you the correct answers. Of course, Google is commonly known as a universal cure for many doubts, but handling the problem yourself is much more rewarding. Recently I came across some simple and interesting examples from Andrew Cumming's book "

Tag: Generators

Useful SQL Patterns: Date Generator

As you start coding in SQL, you will use some statements and techniques over and over again. We call these “SQL patterns”. This series will look at the most common SQL patterns and consider how to use them. SQL patterns, such as the pivot pattern we discussed last week, can save you a lot of time and effort. Suppose you are asked to get a range of days in a financial quarter, but the only records you have are for the start and end dates of each quarter.

Tag: Get started

Join us on Facebook–We Can Learn More Together

We are so happy that you have joined us to learn and develop your SQL skills! We want to invite you to a new Facebook group, We Learn SQL. It is a great place for anyone interested in meeting like-minded people who also want to learn about database-related concepts. Learning together is easier, don't you think? Joining this group is a great opportunity to begin sharing your learning experiences with others.

YouTube Tutorials That Actually Teach You Some SQL

YouTube is not just funny cats, music clips, and viral videos. It can also be a mine of knowledge – if you know where to look. Can YouTube tutorials really help you learn SQL? Let's say you're a marketer or an accountant. You work with databases every day. But when it’s time to write a query and get specific data, you need to call someone from IT. Why not learn to do it yourself?

Career Change: From Accountant to Database Designer

How do career changes and life choices impact our future? Can we change the path that's been set for us? And if so, where do we begin? I wouldn't blame you if you thought this article is about change. In a sense, it is—it's in the title, after all. But for me, this article is more about what remains constant. If somebody were to ask me what hasn't changed for me since my childhood, I would know the answer immediately: curiosity.

Forget About Excel, High Five With SQL

Find out why you should forget about Excel and start using SQL even if you're not an IT expert. We'll show you how easy it is to learn SQL, how it can make you work better, and how LearnSQL.com makes the learning process fun. "I Don't Deal With Data" We frequently hear the sentence above from people outside the IT industry. Well, it's not entirely true. Data is now almost everywhere.

A Non-Technical Introduction to Learning SQL on Your Lunch Break

Do you think learning SQL will help you in your career? You are right. SQL is one of the easiest computer languages to learn. These days many non-IT employees have SQL skills and use them to extend their professional capacity. Moreover, more and more companies are encouraging their employees in non-IT areas (like sales, advertising, and finances) to learn and use SQL. One of the benefits of empowering employees with SQL skills is that once you answer one data question, the results will generate a new data question, and then perhaps a cascade of further data questions.

How to Install PostgreSQL on Windows 10 in 5 Minutes

It may look like a complicated task to install PostgreSQL, Oracle, or SQL Server or any other database software, but it really isn’t! These days, most relational database management systems come with installation wizards that make the process much simpler. In this article, we’ll look at how to install PostgreSQL and test that the installation is working. Install PostgreSQL: Steps Involved To install PostgreSQL, we’ll complete the following tasks:

How SQL supports data-driven organization

Typical business users make decisions based on gut feelings, but this can't get them so far. In this article, we'll look at how learning to write basic SQL queries helps your company become a data-driven organization. Businesses face many decisions. Do we increase our advertising budget in one region or the other? Are certain products selling quickly enough? What we should do if they aren't? Most of these decisions are driven by intuition, but organizations that make the most business impact use data-driven decision-making.

Microsoft SQL Server 2017 Installation Step by Step

Microsoft SQL Server is one of the most popular professional database servers on the market. In this guide, I’ll show you all SQL Server 2017 installation steps to help you install it on the Windows operating system together with SQL Management Studio. How to Install Microsoft SQL Server 2017 In this guide, I’ll show you the SQL Server 2017 installation step by step. You can download it for Windows and Linux, but you can’t install Microsoft SQL Management Studio on Linux at the moment, so we recommend you stick to Windows.

How to Begin Running SQL Queries

In this article, I’ll explain how to run a SQL query to help you execute your first one. Let’s jump right in! Running SQL queries for the first time is not a complex task, but it can seem intimidating at first if you’re a complete beginner. But once you get past that initial roadblock, you’ll be able to focus on learning SQL and writing more interesting queries to meet your business needs.

How to Use a SQL Wildcard

SQL wildcard allows us to filter data matching certain patterns in SQL. We use SQL wildcards with the LIKE operator in the WHERE clause of a query to filter data. In this beginner’s article, we’ll look at everything you need to know about basic SQL wildcards. If you like playing cards, then you know that wildcards can substitute any other card in your deck. Similarly, SQL wildcards can substitute one or more characters.

Our Picks for 2020’s 7 Best Online SQL Schools

If you’re looking for the best online SQL courses but aren’t sure where to start, you’re in the right place. I evaluated the top 7 ranked SQL schools available online to help you find the right solution. While summer is a great time to relax and get away from work, it’s also an excellent opportunity to learn new skills – like SQL! Thanks to SQL schools putting their courses on the internet, learning new tech skills is super easy and you can choose from a variety of formats to suit your needs.

Why Learn SQL Over the Summer

Think summer is reserved for flying to warm places and hanging out at the beach? Sure! But it's also a great time to learn new skills that you haven't had time for. If you recently graduated from high school and want to get a head start on computer programming for college, learning SQL over the summer is a great opportunity. You have nothing to lose and everything to gain—SQL is actually really easy to learn, especially with so much free time over the summer.

Here’s Why You Should Learn SQL

Why learn SQL? We asked our users about it. This is what we’ve learned. At LearnSQL.com, we help people with no computer science background to understand the core concepts of databases and data science. For example, we teach users how to extract the most important data from a database to build simple reports and how to understand key statistical metrics in data analysis. We love to provide easy-to-understand examples that thoroughly depict complex technical concepts.

How to Start Thinking in SQL

Thinking in SQL will help you understand what SQL queries do, how to create and change them, and how to create reports from the data you obtain. If you want to know how to write better SQL queries, you have to change the way you think about the code. One of the greatest skills you can have in SQL programming is the ability to change an existing SQL query so you get the results you need.

Introduction to Reporting with SQL — the Ultimate Tutorial for Business Professionals

Working with the financial aspects of large and small enterprises can be a daunting task for a business professional. In this article, we'll look at several ways of constructing the perfect SQL report. You've probably already heard about SQL from your colleagues or in other areas of your career. If you're here, you've likely concluded that learning SQL will make your professional life easier – and you're right!

5 Great Benefits of Learning SQL

If you want your business to succeed in 2017, it’s absolutely critical that you understand your data; this is why you should get acquainted with SQL ASAP. But there are other reasons to learn it that may not be obvious. In this article, I’ll show you 5 huge benefits of learning SQL! Don’t fall for the common trap—analyzing data isn’t just a concern for those competing at national or corporate levels.

Why Is SQL Worth Learning?

Nowadays, data is gathered from a variety of sources, and information is of great value to organizations. However, with an increasing amount of data comes the need for databases that can store information for retrieval and analysis by trained specialists. That’s where Structured Query Language comes in. Is SQL worth learning? In this article, I’ll explain why it definitely is. Relational databases, which logically group information into chunks, are basically used to store and organize large amounts of data.

SQL Mythbuster – 5 Reasons Why No One Should Be Afraid of SQL

Anyone can learn SQL. It’s not as hard as you think! In today’s world, even those in non-technical jobs need some technical skills. And you don’t have to be a hard-core nerd to get these skills. Let me tell you my own story. A few years ago, I wasn’t considering learning SQL or anything else that I labelled “technical”. My background is in sociology, journalism, and scriptwriting, and I thought computer languages were pretty sci-fi.

5 Books That Will Grow Your SQL Skills

Which books will help you build your database skills? We look at five awesome SQL books. There’s a common saying that “all wise men read books”. I would say that all professionals read books – particularly those related to their field. There are many books about databases and SQL; most are tied to specific vendors (DB2, Oracle, MS SQL) but there are also plenty that are vendor-neutral. In this article, I’m going to review a few books that I would recommend to SQL learners at various levels of proficiency.

The Complete Beginner’s Guide to SQL Fundamentals

LearnSQL.com is a great place to learn SQL. If you’re a complete beginner, it’s best to have an overview of what SQL is, what a database is, and how they work together. In this article, you’ll find a complete guide to SQL fundamentals. SQL Fundamentals: Database Let’s begin our guide to SQL with basic definitions. You might have already heard that SQL is used with databases. What exactly is a database?

How to Learn SQL: 6 Ideas for Newbies

Learning a new skill can be a daunting task, especially in programming. SQL is not immune to this. Luckily, with the Internet and the explosion of programming-related information out there, there are a lot of options you can use to undergo your SQL training! But we then come to a new roadblock. Where to begin? How will we know which option is best for our budget, skill level, and schedule?

Tag: Get started with sql

SQL Indexing 101

Indexes are one of the most misused and misunderstood entities in physical database design. A good understanding of indexes and how they solve database performance problems is necessary for any database novice. In this article, we'll look at basic database indexes and their role in database development. To picture what an index is, consider a textbook. At the end of most textbooks is an index listing all the terms one can find in the text and the pages on which they appear.

Tag: Group by

What Is GROUP BY in SQL?

GROUP BY is a great SQL feature that allows you to perform powerful calculations on grouped data. Do you want to learn how to get powerful insights from your data? Would you like to know what GROUP BY does and when you should use it? If your answer is yes, keep reading. In this article, you will learn exactly that. Why You Need GROUP BY In today's digitized world – no matter what business you are in – database tables are usually huge, with millions of records.

Why Aren’t SQL Window Functions Allowed in GROUP BY?

It’s true – the SQL order of operations means window functions aren’t allowed in GROUP BY. But you can use them anyway with this special trick. SQL window functions are one of the language’s most powerful features. However, the syntax of window functions is not easy to master. It has lots of details that can cause beginners to stumble. One of the most common traps is trying to use window functions in GROUP BY.

7 Common GROUP BY Errors

Are you making these errors with GROUP BY in SQL? Find out what they are, how to avoid them, and how to fix them. SQL’s GROUP BY statement can quickly uncover powerful data insights. At first, using GROUP BY can seem easy – e.g. when creating basic SQL reports that you’ll present to business decision-makers. But while learning this powerful feature, you could become trapped in weird errors or get incorrect results caused by improperly written GROUP BY statements.

An Overview of Aggregate Functions in SQL

Aggregate functions are commonly used in SQL. This article will lead you through their use and show examples of how they work. SQL aggregate functions are a useful tool, especially for creating reports. They’re not difficult to understand, especially if you have some experience with Excel or similar programs. You’ve probably used aggregate functions like SUM or AVERAGE in a spreadsheet. Even if you only occasionally use them, knowing aggregate functions can help you better understand your data and work more efficiently.

How to Use CASE WHEN With SUM() in SQL

This article will teach you what a CASE WHEN expression is in SQL and how to use it with a SUM() function and a GROUP BY statement. The examples are included to bolster your understanding. Knowing how to use a CASE WHEN expression in SQL adds insight into the exciting possibilities in SQL. It elevates you from a simple user who depends on what SQL returns, to a user who is more in command and who sets specific criteria in SQL.

SQL Course of the Month – GROUP BY Extensions in SQL

Do you want to develop your SQL skills? Do you want to get more out of your data and prepare better reports and summaries? The answer is learning to use SQL’s GROUP BY extensions. But how should you go about this? I asked the same question to Agnieszka Kozubek-Krycuń, Vertabelo’s Chief Content Officer. As she explains, the secret is in this November’s free SQL Course of the Month: GROUP BY Extensions in SQL.

What is the Difference Between COUNT(*), COUNT(1), COUNT(column name), and COUNT(DISTINCT column name)?

Have you noticed there are different variations of the SQL COUNT() function? This article explains the various arguments and their uses. As a SQL user, you’re probably quite familiar with the COUNT() function. Even though it’s relatively simple, it can be used in several different ways. Each way has a very different use. I imagine you’ve seen code that contains the function COUNT(*) or COUNT(1). You’ve probably also seen some other uses of the COUNT() function, such as COUNT(column name) and COUNT(DISTINCT column name), even if you haven’t used them.

How to Fix a 'Not a GROUP BY Expression' Error

Whether you are an experienced SQL user or only a beginner, your SQL queries may return errors. The accompanying messages are supposed to help you fix them; however, sometimes the messages are not very helpful. The Oracle message “Not a GROUP BY expression” is one such example. Let’s review what this is about and how to fix it. We are going to assume some basic understanding of how GROUP BY works.

GROUP BY in SQL Explained

The SQL GROUP BY statement is easy to use, but it can be hard to master. Learn what you can do with GROUP BY, how it works, and how to use it with aggregate functions. GROUP BY is one of the basic SQL tools. However, it might be difficult for beginners to understand how GROUP BY works and how it is used to compute statistics with different aggregate functions. In this article, I’ll use several examples to show exactly how GROUP BY organizes rows and how aggregate functions can be used to calculate statistics on one or more columns.

How to Find Duplicate Values in SQL

Duplicate records waste time, space, and money. Learn how to find and fix duplicate values using SQL’s GROUP BY and HAVING clauses. Database best practices usually dictate having unique constraints (such as the primary key) on a table to prevent the duplication of rows when data is extracted and consolidated. However, you may find yourself working on a dataset with duplicate rows. This could be because of human error, an application bug, or uncleaned data that’s been extracted and merged from external sources, among other things.

How Does SQL GROUP BY Work?

Grouping results is a powerful SQL feature that allows you to compute key statistics for a group of records. GROUP BY is one of SQL’s most powerful clauses. It allows you to see data in a new way and find key metrics (like the average, maximal, and minimal values in a group of records). Without GROUP BY, all the results we obtain are oriented to records. With GROUP BY, we can create groups of records and calculate metrics on each group.

5 Examples of GROUP BY

When you start learning SQL, you quickly come across the GROUP BY clause. Data grouping—or data aggregation—is an important concept in the world of databases. In this article, we’ll demonstrate how you can use the GROUP BY clause in practice. We’ve gathered five GROUP BY examples, from easier to more complex ones so you can see data grouping in a real-life scenario. As a bonus, you’ll also learn a bit about aggregate functions and the HAVING clause.

What Is the Difference Between WHERE and HAVING Clauses in SQL?

As the amount of data in the world grows day by day, the need increases for managing and querying data efficiently. SQL offers ways to manipulate and query data at any scale. As an important part of this, the WHERE and HAVING clauses allow you to filter data as you need, but they are not the same. We will explain the differences between them in detail. One of the most common tasks in manipulating and querying data is filtering using the WHERE and HAVING clauses.

The SQL HAVING Clause Explained

What is the SQL HAVING clause? Why do you need it, and where do you use it? We’ll explain HAVING in detail. HAVING is a very common clause in SQL queries. Like WHERE, it helps filter data; however, HAVING works in a different way. If you are familiar with the GROUP BY clause and have only heard about HAVING – or if you’re not familiar with HAVING at all – this article is what you need.

Using GROUP BY in SQL

Now that you know SQL’s core commands, power up your queries with the GROUP BY clause and aggregate functions. GROUP BY is a SQL clause that arranges data into groups based on a common value (or values). It is widely used to obtain summary information for large datasets as well as for computing basic aggregate statistics. Once you have grasped SQL’s basic commands like SELECT, WHERE, and JOIN, mastering the GROUP BY clause can help you implement your SQL knowledge in real-world business intelligence scenarios.

What Is the Difference Between a GROUP BY and a PARTITION BY?

Window functions are a great addition to SQL, and they can make your life much easier if you know how to use them properly. Today, we will address the differences between a GROUP BY and a PARTITION BY. We’ll start with the very basics and slowly get you to a point where you can keep researching on your own. PARTITION BY vs. GROUP BY The PARTITION BY and the GROUP BY clauses are used frequently in SQL when you need to create a complex report.

Difference between GROUP BY and ORDER BY in Simple Words

For someone who is learning SQL, one of the most common places to get stuck is when learning the GROUP BY command. GROUP BY and ORDER BY are two important keywords in SQL that we use to organize data. The difference between GROUP BY and ORDER BY is that ORDER BY is more simple than GROUP BY and is usually introduced early in an SQL course. Sometimes, people are quite confused over these two concepts (SQL ORDER BY vs.

SQL Hacks To Control Family Budget On Black Friday Weekend

If you’re in the US, chances are you’ve been eagerly awaiting the approach of Black Friday just as much as Thanksgiving. Though the shopping frenzy takes hold of nearly everyone, some people have to stick to their budgets and shop prudently. In this article, we’ll take a look at how generating an SQL report can help you track how much your family spent shopping on Black Friday. Storing Black Friday Purchases in a Database Before we can create an SQL report, we first need some data we can use.

A Beginner’s Guide to SQL Aggregate Functions

Aggregate functions are powerful SQL tools that compute numerical calculations on data, allowing the query to return summarized information about a given column or result set. These functions can be used in conjunction with the GROUP BY statement. Let’s see how they work using some easy examples. SQL Aggregate Functions Suppose we have users residing in a city, and we store their information in two tables. These tables and their relationship are shown below:

Getting the Hang of the GROUP BY Clause

GROUP BY is an important part of the SQL SELECT statement. But new SQL coders can run into some problems when this clause is used incorrectly. Here’s how to avoid those issues. You’re learning SQL. You know how to SELECT some data FROM a table and how to filter the data with a WHERE clause. You can process the data using aggregate functions (MIN, MAX, SUM, AVG, and others). But when you’re dealing with a lot of data, you may need to narrow it down even more.

GROUP BY Clause: How Well Do You Know It?

The database can do different kinds of computations: it can add and subtract, multiply and divide, it can do computations on dates, it can count rows and sum row values, and so on. It can also do quite sophisticated statistics. The GROUP BY clause is the most basic way to compute statistics in SQL. It can be quite tough for beginners but it is really powerful. Let's look at the details of the GROUP BY clause, starting with the basics.

Tag: Guide

SQL Terms Beginners Should Know - Part 3

This is the third part of my list of essential SQL terms for beginners. In the first, you learned what tables, relational databases, and queries are. In the second part of the tutorial, I told you about aliases, SQL JOINs, primary keys, and subqueries. Now, it's time for more advanced database terms. But don't be afraid! I won’t crush you with scientific definitions. I will explain everything simply so that you can easily understand.

SQL Terms Beginners Should Know – Part 2

This is the second part of my list of essential SQL terms for beginners. In the first, you learned what a table, relational database, and query are. Now, it's time for more advanced database terms. But don't be afraid! I won’t crush you with scientific definitions. I will explain everything simply so that you can easily understand. If you want to review the basic SQL terms, see my previous article, SQL Terms Beginners Should Know.

SQL Terms Beginners Should Know

Have you started learning SQL? Do you feel a little lost in the maze of new words and ideas? Here’s a list of 10 absolutely essential SQL terms for beginners. When you start learning SQL, there’s a lot to process. And some of it – even basic SQL terms – gets lost in the shuffle. If this sounds like you, bookmark this article; it will be a handy reference.

Five Essential Features of a Good SQL Course: What to Look for When Choosing a Course for You

There are many different platforms offering SQL courses. If you’re a beginner, it may be difficult to choose the right one for you. Find out what we think are the essential features of a good SQL course. Remember, if you make a poor choice at the beginning, you may get discouraged or get into bad habits that will impact your work down the line. What Is SQL? SQL, or Structured Query Language, is a programming language you use to talk to databases.

The Most Popular Databases in 2020

Which database solution is currently most popular? Which SQL dialect should you study? In this article, I’ll share the results of my research and my personal experience. Here are the databases that are worth learning SQL to use. First, let's answer some simple questions: Is SQL still useful? Is it worth learning? If you complete an online SQL course, will it make your work easier? The answer is YES! Why?

Top 10 Laptops for Learning SQL in 2020

If you want to learn SQL, you’re going to need a device that’s portable and powerful. I recommend a laptop. Here are the features you’ll need, as well as my picks for laptops to get you learning SQL in 2020! I must admit that browsing Amazon’s computer offers or entering any computer store can give you a headache. So many models, with so many options! They differ in components, workmanship, battery life, and screen size and resolution.

What Is a SQL Dialect, and Which one Should You Learn?

SQL, standard SQL, SQL Server, MySQL, PostgreSQL, Oracle, … You’d like to learn SQL, but you feel overwhelmed with keywords and you don’t know where to start. Let’s explain what each of those terms mean. SQL Is the Language for Talking to Databases A database is a computer program that can store and process large amounts of data. There are many different vendors of databases. PostgreSQL, MySQL, Oracle, and SQL Server are all database products by different vendors.

How to Publish a LearnSQL.com Course Certificate on LinkedIn

LinkedIn draws both job seekers and recruiters. Showcasing your knowledge, skills, and experience on this professional networking site can lead to great opportunities. We know this well at LearnSQL.com. Have you finished one of our courses? Great! Tell your future employer about what you have learned. Here's a step-by-step how-to guide for publishing a course certificate on LinkedIn. I will show you how easy it is to publish a LearnSQL.

Last-Minute Preparation Tips for a Database Class Exam

Getting to learn SQL is fun. You don’t really need to spend much time to understand some basic SQL concepts and use them fluently. If you’re a student facing your first database class exam soon, we’ve got you covered. In this article, we explain what you should focus on while learning SQL and studying for an entry-level database exam. Check your knowledge with our 10 sample questions and discover where you can find more SQL practice.

Top 5 Programming Languages to Learn Alongside SQL

If you already know or are about to learn SQL, you’re well on your way to being a sought-after database administrator, database engineer, or just a general database whizz kid! SQL is a modern, widely-used language that finds application in almost every industry. There is no shortage of jobs with SQL. But what if you want to branch out and learn another language to complement your SQL knowledge and skills?

Advanced SQL Courses for Data Analysts – A Complete Review

Even data analysts who already know SQL need to keep their skills sharp. Where can you find the best advanced SQL courses for data analysts? Check out our review of the top online sources! In this article, I present a list of online SQL courses for data analysts. These courses are offered by various platforms. Why wait? Let’s jump right in! 8 Advanced SQL Courses for Data Analysts Let's take a closer look at these courses to decide which platform will be better for you in learning SQL.

What SQL Practice Do You Need to Prepare for a Technical Job Interview?

You’ve scored yourself an interview for an SQL-related job. Nice work! But perhaps uncertainty is creeping in as your interview date looms closer. Do you know enough SQL to make the cut? What questions are you likely to be asked? What SQL practice should you be doing before your interview? Almost all SQL job candidates go through exactly the same nerve-wracking process. Here at LearnSQL.com, we have the lowdown on all the SQL practice and preparation you’ll need to ace those interview questions and take your career to the next level.

Is SQL Worth Learning?

We’re in the 21st century. These are the “ultimate data times” in which loads of information on all kinds of things is available. We want to explore this info even more, slice and dice it, understand where it comes from and what triggers it. With such large amounts of data coming in, people have discovered that spreadsheets aren’t enough. There’s a need for a greater solution, something like a spreadsheet on steroids.

Top 3 Platforms to Learn SQL Online: A Complete Comparison

Do you want to learn SQL online? Where do you start? There are many choices on the internet, and it can be hard to decide. But don’t worry—I tested and compared three major platforms to help you find the best place to learn SQL online! E-learning is on the rise. It gives us infinite possibilities of growing our professional careers without leaving our homes. And increasing our competencies is especially important now that the labor market has become dynamic and unstable.

Choose the Best Way to Learn SQL

SQL has become a hot topic in the professional world, and many resources have appeared both online and offline for learning SQL. It’s easy to get lost in the jungle of books, tutorials, and courses. Which resources do you choose? If you want to know how to learn SQL quickly and effectively, take a look at my list. There are many reasons for learning SQL. We asked our users about them and learned that there was no universal motive.

50 Best Resources for Learning SQL in 2020

Do you want to know where to learn SQL? We’ve got you covered with the ultimate list of 50 resources for learning SQL, including the best SQL courses, tutorials, books, and much, much more! Learning SQL can be hard enough without wading through thousands of websites and articles. So, we thought we’d do you a solid and put the top SQL resources here in this handy slice of the internet.

How to Stay Healthy When Learning SQL

So, maybe you’re learning SQL. Congratulations! Or maybe you already work as a data analyst, DBA, or data scientist. That’s great too! Either way, you are most likely spending hours in front of a computer. I will give you tips on how to avoid bad habits and take care of your health while learning and/or working with SQL. Have you ever wondered how sitting in front of a computer affects your health?

What Programming Language Should You Learn?

If you've ever been wondering which programming language you should learn first, you know that's a tough nut to crack. It’s especially difficult if you are new to IT and programming. In this article, I give suggestions for what to learn first and what perspectives each language can give you in IT. There are hundreds of programming languages, and new ones are showing up all the time. Getting to know all of them is simply impractical and impossible.

How to Study Online: 5 Steps to Becoming an Effective Learner

If you suffer from procrastination or lack of motivation, you’re not alone. We have some online learning tips to make your learning journey smoother and more enjoyable. One of the best things about being an adult is that we can do what we want: go to sleep late at night, party until morning, eat junk food. Besides all those small pleasures, as adults we are responsible for ourselves, our choices, and our mistakes.

How to Install PostgreSQL on Windows 10 in 5 Minutes

It may look like a complicated task to install PostgreSQL, Oracle, or SQL Server or any other database software, but it really isn’t! These days, most relational database management systems come with installation wizards that make the process much simpler. In this article, we’ll look at how to install PostgreSQL and test that the installation is working. Install PostgreSQL: Steps Involved To install PostgreSQL, we’ll complete the following tasks:

Tag: Having

SQL HAVING Tutorial

Learn how to use the SQL HAVING clause to filter groups using your own specified conditions. The SQL HAVING clause is often a challenging concept to grasp, especially for beginners. Additionally, its specific use cases can be difficult to visualize without specific examples based on real-world datasets. In this tutorial, you will learn how to apply the SQL HAVING clause to filter groups of records based on specified conditions. You’ll see examples where we apply this concept to solving business problems on a realistic dataset.

HAVING vs. WHERE in SQL: What You Should Know

This article is about SQL’s WHERE and HAVING clauses. Both clauses are part of the foundations of the SQL SELECT command. They have similar uses, but there are also important differences that every person who uses SQL should know. Let’s see what’s behind the HAVING vs. WHERE debate. In this article, we’ll suppose we work for a government social agency supporting people or families whose income is below a certain threshold.

Tag: Health

How to Stay Healthy When Learning SQL

So, maybe you’re learning SQL. Congratulations! Or maybe you already work as a data analyst, DBA, or data scientist. That’s great too! Either way, you are most likely spending hours in front of a computer. I will give you tips on how to avoid bad habits and take care of your health while learning and/or working with SQL. Have you ever wondered how sitting in front of a computer affects your health?

Tag: How to

Practical Ways to Improve the Performance of SQL Queries

Knowing how to improve SQL query performance is an important skill, especially when working with with large databases. In this article, you'll learn how to write more efficient SQL queries to get results faster. The biggest difference between SQL and other languages is that SQL is a non-procedural language. In a non-procedural language you specify the results that you need but not the methods used to get it. The advantage of a non-procedural language is that it is easier to write programs, therefore it is common for non-programmer business users to generate reports from SQL queries.

SQL Filtering 101

Sometimes, SQL queries return lots of data you don't need. In this article, we'll look at a simple example of filtering SQL queries to reduce the complexity of your data. The key to learning how to filter data in SQL is understanding the very basics of Boolean algebra. That's just a fancy term mathematicians use to describe expressions involving logical values (true/false) and their associated operators (and, or, not, etc.

Improving Query Readability with Common Table Expressions

What is a Common Table Expression, or CTE? Where do you use them, and why? This post answers your questions. Simply put, Common Table Expressions (also known as WITH clauses) are essentially named subqueries. They also provide additional features like recursion. If you're new to subqueries, I recommend you read the SQL Subqueries article before continuing. The main purpose of Common Table Expressions is to improve the design and readability of an SQL statement.

SQL Development? Structured Query Language and Apps

You know about using SQL with databases. How does SQL fit in with app development? Is there anything like SQL development? In this post, we look at the app development process, how it intersects with modeling a database, and what developers can do with SQL outside of their app. Obviously, the beginning of this process is defining your app — what it does, who it is for, how it will function and look, etc.

Performing Calculations on Date- and Time-Related Values

Relational databases support several date and time data types. In this article, we'll look at several arithmetic operations we can do on these types. These operations are logical and understandable, even for the beginning SQL coder. Let's first briefly explain the main data types used for dates and times. Keep in mind that data types may differ by database engine, so check your database documentation for specifics before you start working with them.

Getting the Hang of the GROUP BY Clause

GROUP BY is an important part of the SQL SELECT statement. But new SQL coders can run into some problems when this clause is used incorrectly. Here’s how to avoid those issues. You’re learning SQL. You know how to SELECT some data FROM a table and how to filter the data with a WHERE clause. You can process the data using aggregate functions (MIN, MAX, SUM, AVG, and others). But when you’re dealing with a lot of data, you may need to narrow it down even more.

Refine Results with SQL Set Operators

Using UNION, UNION ALL, EXCEPT, and INTERSECT to manage SQL query results. The function of SQL set operators is pretty simple; they allow us to combine results from different SQL queries into one result set. The best way to understand how set operators work is to use visual methods like the Venn diagram. For those of you not familiar with Venn diagrams, they are two circles that represent items or collections of items.

6 Common SQL Syntax Mistakes All Learners Make

We all make mistakes when learning a new language – especially at the beginning. New words, complicated grammar... Everyone needs time to master a language. But when we get immediate feedback, we can progress more quickly. The same goes for learning SQL. In this article, we'll look at 6 common SQL syntax mistakes most SQL learners make. Mastering SQL Queries Interactive SQL courses are one way to get immediate feedback on your queries.

8 Tips Absolute Beginners Can Use to Fix SQL Queries

Code errors are common – and frustrating. And when you're just learning SQL, it can be very challenging to find and fix your mistakes. In this post, we'll show you eight ways to solve or eliminate common SQL coding errors. Today, we'll talk about some tips the SQL beginner can use to avoid several common errors. These tips work in any database environment. As we go along, we'll be showing some error messages.

Five Common SQL Syntax Errors

As you learn SQL, watch out for these common coding mistakes You’ve written some SQL code and you’re ready to query your database. You input the code and …. no data is returned. Instead, you get an error message. Don’t despair! Coding mistakes are common in any programming language, and SQL is no exception. In this post, we’ll discuss five common SQL syntax errors people make when writing code.

SQL Errors: Five Common SQL Mistakes

As you learn SQL, watch out for these common coding mistakes You’ve written some SQL code and you’re ready to query your database. You input the code and …. no data is returned. Instead, you get an error message. Don’t despair! Coding errors are common in any programming language, and SQL is no exception. In this post, we’ll discuss five common mistakes people make when writing SQL. Watch Your Language (and Syntax) The most common SQL error is a syntax error.

Tag: How to in sql

Practical Ways to Improve the Performance of SQL Queries

Knowing how to improve SQL query performance is an important skill, especially when working with with large databases. In this article, you'll learn how to write more efficient SQL queries to get results faster. The biggest difference between SQL and other languages is that SQL is a non-procedural language. In a non-procedural language you specify the results that you need but not the methods used to get it. The advantage of a non-procedural language is that it is easier to write programs, therefore it is common for non-programmer business users to generate reports from SQL queries.

How to Begin Running SQL Queries

In this article, I’ll explain how to run a SQL query to help you execute your first one. Let’s jump right in! Running SQL queries for the first time is not a complex task, but it can seem intimidating at first if you’re a complete beginner. But once you get past that initial roadblock, you’ll be able to focus on learning SQL and writing more interesting queries to meet your business needs.

SQL Indexing 101

Indexes are one of the most misused and misunderstood entities in physical database design. A good understanding of indexes and how they solve database performance problems is necessary for any database novice. In this article, we'll look at basic database indexes and their role in database development. To picture what an index is, consider a textbook. At the end of most textbooks is an index listing all the terms one can find in the text and the pages on which they appear.

How to Use a SQL Wildcard

SQL wildcard allows us to filter data matching certain patterns in SQL. We use SQL wildcards with the LIKE operator in the WHERE clause of a query to filter data. In this beginner’s article, we’ll look at everything you need to know about basic SQL wildcards. If you like playing cards, then you know that wildcards can substitute any other card in your deck. Similarly, SQL wildcards can substitute one or more characters.

SQL Filtering 101

Sometimes, SQL queries return lots of data you don't need. In this article, we'll look at a simple example of filtering SQL queries to reduce the complexity of your data. The key to learning how to filter data in SQL is understanding the very basics of Boolean algebra. That's just a fancy term mathematicians use to describe expressions involving logical values (true/false) and their associated operators (and, or, not, etc.

Why Learn SQL Over the Summer

Think summer is reserved for flying to warm places and hanging out at the beach? Sure! But it's also a great time to learn new skills that you haven't had time for. If you recently graduated from high school and want to get a head start on computer programming for college, learning SQL over the summer is a great opportunity. You have nothing to lose and everything to gain—SQL is actually really easy to learn, especially with so much free time over the summer.

Key Insights for Mastering SQL Queries Using Tinder Data Example

Going from zero to one can be daunting in any endeavor. The same is true for learning new programming languages, even simple ones like SQL. In this article, we’ll take a look at some key insights that will help you understand the nuances of mastering SQL queries. If you’ve never used SQL, you’re in the right place. When learning anything new, you’ll find that there are always some key insights or tips that can help you on your way.

Improving Slow Query Performance: When Runtime Matters

As SQL users, we usually focus on writing queries that return correct results. However, there are more things to consider when you're writing a query; one of them is query performance. In this article, we'll look at some examples where query response time is critical. Scene One: 911 Call Center Let's suppose we're at a 911 call center, when the phone rings. One of the operators answers the call; a witness reports that a man has been shot.

Converting Subqueries to Joins

Not all queries are alike, especially in terms of performance. In this article, we'll look at how you can convert SQL subqueries to joins for improved efficiency. When should I use SQL subqueries? Great question! Unfortunately, there's no concrete answer. SQL beginners tend to overuse subqueries. Typically, once they find that SQL construction works in one situation, they try to apply that same approach to other situations. It's only natural.

Essential SQL Terms to Know for Beginners and Pros

Working with databases can seem daunting to a non-technical person. Right away, you’re bombarded with new terms that make your head spin. Database, database instance, table, SQL and others are some of the basic terms that you need to understand just to have a normal conversation with your technical colleagues. In this article, we’ll explore some basic SQL database terminology you need to know to succeed. Imagine you’re attending a meeting with the development staff and suddenly feel as if you’re listening to white noise.

Learn to Write a SQL Correlated Subquery in 5 Minutes

If you’re familiar with the famous Russian nesting doll, then SQL correlated subqueries should be a peace of cake to understand—subqueries are just queries nested within queries. An SQL subquery is often called an “inner” query; the main query is usually called the “outer” query. This article covers everything you need to know about correlated subqueries. What Exactly is a SQL Correlated Subquery? A correlated SQL subquery is just a subquery that is executed many times—once for each record (row) returned by the outer (main) query.

New LearnSQL.com Online Practice – Solve Basic SQL Questions with the SQL Practice Set

If you’re looking to retrieve any kind of information from a database, you need to speak its language. But querying databases is an art—and it demands practice. That’s why we created our SQL practice set: a pack of SQL online practice exercises meant to help you master your skills. We spend a lot of time not only developing new courses but also speaking with our users and learning what they expect from SQL online practice exercises.

How to Become a Database Analyst

Curious about becoming a database analyst? Maybe you've taken some database courses at university and they really struck a chord. Or maybe you learned online. Now you're thinking about making a career out of working with databases. Where would you start? What should you expect at each phase of your professional development? In this post, we'll explore the challenging and exciting world of databases analysis. We'll go from the very beginning of a career to the apex of professional success.

Extracting Data From a String: SPLIT_PART in PostgreSQL

Learn how to use split_part in PostgreSQL to extract data from strings. Quite often, we’d like to extract parts of a string when working with text values. A common example is when we have a full name and need to retrieve only the last name. In this article, we’ll examine how to do it using split_part in PostgreSQL, i.e. a string-related function that can be used to extract a substring.

How to Remove Junk Characters in SQL

Unwanted characters in text data can be a bit of a pain, but there’s an easy way to fix them. Scroll down to learn how to remove junk characters in SQL in the easiest way! Sometimes, we’ll find unwanted characters inside our string data because our SQL queries didn’t work as expected. Moreover, these extra characters may sometimes be invisible, which really complicates things. In this article, we’ll examine some string-related SQL functions that can handle unwanted characters—visible or not!

How to Solve Capitalization Data Quality Issues

Misspelled names, typos, and text data quality issues in your database? Power up your queries! Use SQL string functions to address data quality issues related to capitalization. Sometimes, our SQL queries don't work as expected because of data quality issues. In this article, we will examine some string-related SQL functions that can correct data quality issues related to capitalization. We'll be using PostgreSQL in our examples, but similar functions are available in most database engines.

18 Useful Important SQL Functions to Learn ASAP

Beginning with SQL: Useful Functions to Master Learning a new programming language can seem intimidating. Like any other language, a programming language has a large vocabulary that you need to master. In this article, we'll look at some of the most useful SQL functions that you need to know. There are many useful SQL functions for working with different data types. Once you practice with some of the most common ones, you'll gain enough confidence to move on to more advanced material.

Simplify SQL Code: Recursive Queries in DBMS

Hey SQL users! Are you repeating the same query in every report? Are your queries getting too complicated? Use recursive queries to simplify SQL code! Too many SQL reports can lead to clutter on your desktop and in your head. And is it really necessary to code each of them separately? Ad-hoc queries can share much of the same SQL code with managerial reports and even regulatory reports. Suppose you’ve been writing basic SQL code for a while.

Digging Into Data: Explore and Analyze Survey Results With SQL

Excel is a powerful beast that lets you analyze complex data. Yet, operating on big chunks of data can sometimes be a daunting task. Let's take a look at how SQL can help. Today, we'll tackle a common problem with importing data to an SQL database, using a real-life example. Suppose your company conducted a survey on the most popular programming trends and preferences, striving to meet the expectations of its users.

SQL Hacks To Control Family Budget On Black Friday Weekend

If you’re in the US, chances are you’ve been eagerly awaiting the approach of Black Friday just as much as Thanksgiving. Though the shopping frenzy takes hold of nearly everyone, some people have to stick to their budgets and shop prudently. In this article, we’ll take a look at how generating an SQL report can help you track how much your family spent shopping on Black Friday. Storing Black Friday Purchases in a Database Before we can create an SQL report, we first need some data we can use.

SQL Window Functions By Explanation

In our previous post, we explained how SQL window functions work by example. We started with some very simple, basic functions. Let's extend it by explaining subclauses in window functions. SQL window functions are a great way to compute results from a set of rows rather than a single row. As you know from our first article, the "window" in window function refers to the set of rows. We showed you some examples of simple window functions like RANK and LEAD.

The 5 Highest Paying Jobs That Use SQL

IT provides a wide and growing job market, offering many excellent opportunities in both career development and earning potential. Today we’ll take a look at several very interesting types of database jobs that use SQL. Every year, many in the work force set their sights and aim for new and better jobs. When it comes to jobs, “better” means different things to different people, but earning potential is almost always a top priority.

Four Reasons You Must Learn SQL in Data Science

Is SQL important for data science? It certainly is! This language can help you build a foundation for your analytical career. Let’s see how you use SQL in data science. Data science is hot right now. What if you could predict the next market crash? Or contain the spread of Ebola? Or accurately predict a health crisis months or even years before it happens? Data scientists are working hard on these kinds of projects, and they are earning healthy salaries in the process.

SQL Mythbuster – 5 Reasons Why No One Should Be Afraid of SQL

Anyone can learn SQL. It’s not as hard as you think! In today’s world, even those in non-technical jobs need some technical skills. And you don’t have to be a hard-core nerd to get these skills. Let me tell you my own story. A few years ago, I wasn’t considering learning SQL or anything else that I labelled “technical”. My background is in sociology, journalism, and scriptwriting, and I thought computer languages were pretty sci-fi.

Introducing SQL Set Operators: Union, Union All, Minus, and Intersect

Ever heard terms such as union and intersection in SQL? They're examples of set operators, and they come in handy when you need to combine information from multiple tables or queries. In this article, we'll take a closer look at them. SQL queries let us choose the most important bits from large amounts of information. Of course, we can't expect that all necessary data will be stored in one table.

Improving Query Readability with Common Table Expressions

What is a Common Table Expression, or CTE? Where do you use them, and why? This post answers your questions. Simply put, Common Table Expressions (also known as WITH clauses) are essentially named subqueries. They also provide additional features like recursion. If you're new to subqueries, I recommend you read the SQL Subqueries article before continuing. The main purpose of Common Table Expressions is to improve the design and readability of an SQL statement.

Complete SQL Practice for Interviews

Congratulations! Your SQL skills were strong enough to get you that job interview! Now, if you only knew what SQL questions and practical exercises a recruiter might ask you to do… This article is meant as a SQL practice for interviews. I’ll help you prepare for the SQL and database aspects of your job interview. In a previous article, I explained how can you boost your career by learning SQL.

SQL Development? Structured Query Language and Apps

You know about using SQL with databases. How does SQL fit in with app development? Is there anything like SQL development? In this post, we look at the app development process, how it intersects with modeling a database, and what developers can do with SQL outside of their app. Obviously, the beginning of this process is defining your app — what it does, who it is for, how it will function and look, etc.

The Complete Beginner’s Guide to SQL Fundamentals

LearnSQL.com is a great place to learn SQL. If you’re a complete beginner, it’s best to have an overview of what SQL is, what a database is, and how they work together. In this article, you’ll find a complete guide to SQL fundamentals. SQL Fundamentals: Database Let’s begin our guide to SQL with basic definitions. You might have already heard that SQL is used with databases. What exactly is a database?

Performing Calculations on Date- and Time-Related Values

Relational databases support several date and time data types. In this article, we'll look at several arithmetic operations we can do on these types. These operations are logical and understandable, even for the beginning SQL coder. Let's first briefly explain the main data types used for dates and times. Keep in mind that data types may differ by database engine, so check your database documentation for specifics before you start working with them.

Getting the Hang of the GROUP BY Clause

GROUP BY is an important part of the SQL SELECT statement. But new SQL coders can run into some problems when this clause is used incorrectly. Here’s how to avoid those issues. You’re learning SQL. You know how to SELECT some data FROM a table and how to filter the data with a WHERE clause. You can process the data using aggregate functions (MIN, MAX, SUM, AVG, and others). But when you’re dealing with a lot of data, you may need to narrow it down even more.

Refine Results with SQL Set Operators

Using UNION, UNION ALL, EXCEPT, and INTERSECT to manage SQL query results. The function of SQL set operators is pretty simple; they allow us to combine results from different SQL queries into one result set. The best way to understand how set operators work is to use visual methods like the Venn diagram. For those of you not familiar with Venn diagrams, they are two circles that represent items or collections of items.

6 Common SQL Syntax Mistakes All Learners Make

We all make mistakes when learning a new language – especially at the beginning. New words, complicated grammar... Everyone needs time to master a language. But when we get immediate feedback, we can progress more quickly. The same goes for learning SQL. In this article, we'll look at 6 common SQL syntax mistakes most SQL learners make. Mastering SQL Queries Interactive SQL courses are one way to get immediate feedback on your queries.

8 Tips Absolute Beginners Can Use to Fix SQL Queries

Code errors are common – and frustrating. And when you're just learning SQL, it can be very challenging to find and fix your mistakes. In this post, we'll show you eight ways to solve or eliminate common SQL coding errors. Today, we'll talk about some tips the SQL beginner can use to avoid several common errors. These tips work in any database environment. As we go along, we'll be showing some error messages.

How to Learn SQL: 6 Ideas for Newbies

Learning a new skill can be a daunting task, especially in programming. SQL is not immune to this. Luckily, with the Internet and the explosion of programming-related information out there, there are a lot of options you can use to undergo your SQL training! But we then come to a new roadblock. Where to begin? How will we know which option is best for our budget, skill level, and schedule?

Five Common SQL Syntax Errors

As you learn SQL, watch out for these common coding mistakes You’ve written some SQL code and you’re ready to query your database. You input the code and …. no data is returned. Instead, you get an error message. Don’t despair! Coding mistakes are common in any programming language, and SQL is no exception. In this post, we’ll discuss five common SQL syntax errors people make when writing code.

SQL Errors: Five Common SQL Mistakes

As you learn SQL, watch out for these common coding mistakes You’ve written some SQL code and you’re ready to query your database. You input the code and …. no data is returned. Instead, you get an error message. Don’t despair! Coding errors are common in any programming language, and SQL is no exception. In this post, we’ll discuss five common mistakes people make when writing SQL. Watch Your Language (and Syntax) The most common SQL error is a syntax error.

Tag: Insert

Learn SQL Views in 30 Minutes

Views aren't complicated – if you've got half an hour, we'll get you started writing SQL queries using views! Let's start by answering the question "What is a view in SQL?'. A view is a database object (as is a table, an index, or a stored procedure). Like a table, you can query a view and extract the information in it. It can be used in the FROM clause of a SELECT, and you can reference view columns in clauses like SELECT, WHERE and GROUP BY among other clauses as well.

Using CASE with Data Modifying Statements

What happens when you combine CASE with SQL's data modifying statements? Find out in this article. The CASE expression is a very useful part of SQL and one that you'll employ frequently. We've already covered what the CASE expression does, how to format it, and how to use it in a SELECT statement in "Using CASE to Add Logic to a SELECT". Another article, "How to Sort Records with the ORDER BY Clause"

Tag: Installation guide

Microsoft SQL Server 2017 Installation Step by Step

Microsoft SQL Server is one of the most popular professional database servers on the market. In this guide, I’ll show you all SQL Server 2017 installation steps to help you install it on the Windows operating system together with SQL Management Studio. How to Install Microsoft SQL Server 2017 In this guide, I’ll show you the SQL Server 2017 installation step by step. You can download it for Windows and Linux, but you can’t install Microsoft SQL Management Studio on Linux at the moment, so we recommend you stick to Windows.

How to Begin Running SQL Queries

In this article, I’ll explain how to run a SQL query to help you execute your first one. Let’s jump right in! Running SQL queries for the first time is not a complex task, but it can seem intimidating at first if you’re a complete beginner. But once you get past that initial roadblock, you’ll be able to focus on learning SQL and writing more interesting queries to meet your business needs.

Tag: Jobs and career

Practicing SQL for Your First Day of Work

Your new SQL job is likely to surprise you in many ways. To minimize the risk of getting lost in the jungle of data, I recommend you get some additional SQL practice before your first day. There are special SQL practice sets and projects on the internet to help you prepare. You’ll also get help from your colleagues, as programmers are usually open and supportive. If you’re reading this, you’ve probably heard about the opportunities SQL and data science offer.

The Top 10 SQL JOIN Interview Questions and How to Answer Them

Have you ever wondered what SQL JOIN questions you might be asked in an interview? Do you feel prepared to answer them? This article covers the most common SQL JOIN interview questions and how to answer them. If you are applying for a job as a data analyst or software developer, you will likely be asked about your SQL JOIN knowledge. SQL JOIN clauses are a great topic for interviewers to quiz you on.

Practice SQL Before Interviewing a Potential Employee

Has your company grown to the point that you need to hire an SQL expert? Have you found a candidate for the job? How do you prepare for the interview, especially if you don’t know SQL? Don't worry! Follow our suggestions on how to practice SQL. We have tips and tricks to help you feel confident and find the perfect employee. Who You Want To Hire First of all, you need to know the requirements for the new employee.

How to Boost Your Company With SQL Courses

SQL has the power to supercharge the capabilities and performance of your entire company. But if you don’t dip your toes in the water and give some SQL courses a go, you’ll never realize the vast potential of the language. SQL, or Structured Query Language, is your ticket to expanding the scope and the results of your business or organization, no matter what sector you operate in. Whether you’re the owner or manager of your company or simply an employee interested in improving operations, learning SQL is undoubtedly, unquestionably, for you.

How Will Learning SQL Make You a Better Boss?

Want to improve the performance of your team, of your own, of your department, or of your entire company? Try SQL! Why should you learn SQL? Because it just pays off! What does learning SQL and being a better boss have to do with each other? Being a better manager can make your employees happier while growing your business. When employees feel a sense of fulfillment, they are more motivated to do well.

How Much Do Data Engineers Earn in 2020?

Data engineering is a hot job right now. What does a data engineer do? And just how much do they earn? We’ve done the research for you. If you are reading this, you’re either starting to learn SQL or you already know some and feel it’s time to look around for a SQL job. Maybe you’re in the midst of tackling our Creating Database Structure track. And, let’s be honest, maybe you need some extra motivation to keep on you track.

Why and How to Find Freelance SQL Jobs

If Covid-19 has you all “I-want-to-stop-working-for-the-man-and-enjoy-a-more-fulfilling-life-as-the-master-of-my-own-destiny”, then I’ve got news for you. Not only is it possible to be an SQL freelancer, it’s also a potentially lucrative and liberating career move. It will allow you to work for a diverse range of clients and march to the beat of your own drum. Of course, SQL freelancing isn’t for everyone. You will need a strong sense of self-motivation, some serious hustling skills, and the ability to sell yourself and your services as THE ABSOLUTE BEST all the time, every time - day in, day out.

How to Convince Your Boss That You Need to Start Learning SQL

Learning SQL is a great goal. Now, if you could only convince your boss that it’s good for the company as well as for you ... You’re aware of the benefits of adding SQL to your skill set. You believe that the rewards gained from you learning SQL will also benefit your employer – it’s not just another way for you to develop your professional profile. But how do you articulate this to your boss?

Which Major Companies Use PostgreSQL? What Do They Use It for?

Which companies use the open-source relational database management system PostgreSQL? Find out … and learn why you should be a PostgreSQL user too. You know the blue elephant logo. You have heard that PostgreSQL is a very good solution. But which companies use it? Here is a list of the largest IT and business companies that use PostgreSQL (or Postgres, for short). Multinationals worth billions of dollars can't be wrong, right?

Advanced SQL Interview Questions (and Answers)

Do you want to move to a job that uses SQL? Are you unsure about what to expect during the job interview or how to benchmark your knowledge? This article will give you a good idea of where you stand. If you feel stuck in your job, you’re not the only one. The modern division of work pushes people to perform very specific tasks, expecting them not to look at what's on the other side.

What SQL Practice Do You Need to Prepare for a Technical Job Interview?

You’ve scored yourself an interview for an SQL-related job. Nice work! But perhaps uncertainty is creeping in as your interview date looms closer. Do you know enough SQL to make the cut? What questions are you likely to be asked? What SQL practice should you be doing before your interview? Almost all SQL job candidates go through exactly the same nerve-wracking process. Here at LearnSQL.com, we have the lowdown on all the SQL practice and preparation you’ll need to ace those interview questions and take your career to the next level.

Are There Any Good SQL Courses for Marketers?

Looking for places to learn SQL online and level up your marketing efforts? Check out these SQL courses. Introduction With the help of IT experts, meticulous marketers analyze information to create advertising strategies. This commonplace state of affairs forces the marketer to rely on data experts and sometimes wait for their availability. But what if marketers could pull the data themselves? They can – by turning into a technical marketer.

Types of Database Jobs: Choose One of Them and Start Being Awesome

Do you dream of high earnings and interesting work? Are you fed up with your boss and his or her annoying vacation stories in exotic countries? Is it time to change your job? Why not learn SQL? Here are some examples of the types of database jobs that may lead you to a better life. What types of database jobs use SQL? Here are some examples, but first, a small caveat.

How Will Learning SQL Improve My Daily Work?

Whether you want to boost your professional development, learn in-demand skills, or start something new and interesting, learning SQL will make your life easier in many ways. Are you thinking of learning SQL but aren’t sure if it's a good idea? At first glance, learning SQL may seem completely useless, especially if the industry you are in is not related to IT. But that's not true. Although your position in the company may not imply that you code every day, you can still gain a lot from SQL.

Should I Learn SQL as a Data Analyst?

So, you are a data analyst—someone who relies on data. You like to gather, clean, and transform data and come to conclusions based on data. You are a data detective. Which tool do you choose to do your job in an elegant, reproducible, and simple way? Excel? R? Python? Or should you learn SQL? Stay tuned! In this article, I will explain why SQL is a must-have skill for data analysts.

Top 10 Websites That Will Help You Find the Perfect SQL Job

People learn SQL for many reasons. In my case, I wanted to find a better job that would allow me to earn more and have more free time to pursue my interests. But where do you find such a job? Here is my list of the 10 best websites with database jobs. Although SQL is almost 40 years old, it is appearing in more and more job advertisements. Data has become an essential tool for entrepreneurs, and they are looking for people to squeeze every bit of information from their databases.

Common Entry Level SQL Developer Interview Questions

Have you ever been interviewed for an entry-level SQL position? Are you planning to apply for such a job? This article will help you to know what to expect and prepare for common SQL developer interview questions. After gaining some basic knowledge of SQL and programming, you're probably wondering what to do next. Or maybe you're not wondering! You know that what you've learned will soon disappear if you don't use it regularly.

How to Become an SQL Developer

There is no simple answer to the question “How do you become an SQL developer?” However, if the answer were too complex, there would be no point in writing this article, and yet I’m doing it. So, somewhere along the way, we’ll find the answer. As said in the intro, there is no magic wand that will turn you into an SQL developer. But reading this article will save you some time and help you focus on what is important to achieve your goal.

Why Use SQL Over Excel

SQL is replacing Excel in many fields, and data analysis is certainly one of them. If you are still using Excel as a data analyst, you are missing something very valuable. SQL can make your life easier, as it's more efficient and faster than Excel. So, how and from where can you learn SQL? How Can SQL Help Data Analyst? You can use SQL to help you with the following work:

Career Change: From Accountant to Database Designer

How do career changes and life choices impact our future? Can we change the path that's been set for us? And if so, where do we begin? I wouldn't blame you if you thought this article is about change. In a sense, it is—it's in the title, after all. But for me, this article is more about what remains constant. If somebody were to ask me what hasn't changed for me since my childhood, I would know the answer immediately: curiosity.

Complete SQL Practice for Interviews

Congratulations! Your SQL skills were strong enough to get you that job interview! Now, if you only knew what SQL questions and practical exercises a recruiter might ask you to do… This article is meant as a SQL practice for interviews. I’ll help you prepare for the SQL and database aspects of your job interview. In a previous article, I explained how can you boost your career by learning SQL.

Finding the Perfect SQL Job

So you have some SQL skills and you're looking for a job that will use them. What are your options? SQL is everywhere, and there's a huge demand for people with database management skills. This is especially the case when companies start implementing Big Data solutions and strategies. There's no arguing that SQL is a must-have skill. If you're already proficient, how can you put your expertise to practical use in the job market?

A Day in the Life of a SQL Developer

What is a SQL developer? And what does a SQL developer do? Describing a “typical” day for a SQL developer is not easy. When your daily work is using various technologies to create interesting database-oriented products, very few days are alike! Each day brings a new and intriguing challenge. Nevertheless, I’ll have a go at explaining what everyday things a SQL developer might do. Morning: Arrive at Work What does a SQL developer do after arriving at the office?

Tag: Join

SQL JOIN Tips for Beginners

If you’re a beginner and want to know how to start using SQL JOINs in your queries, you’ve come to the right place. Using the SQL JOIN clause is necessary if you want to query multiple tables. Sooner or later, you’ll have to use more than one table in a query. It’s the nature of relational databases in general – they consist of data that’s usually saved in multiple tables; in turn, these form a database.

What Is an SQL INNER JOIN?

How do you combine data from different tables in one query? An SQL feature called JOIN is the most common operator used to create complex queries. Learn the basics in this article. SQL allows us to select data from more than one table. In fact, the whole idea of using relational databases is selecting data from related tables. And we can use SQL’s JOIN operator to do this. There are many types of JOINs in SQL.

SQL Black Week 2020. See how much you can save!

Wow, have you seen what discounts the LearnSQL.com Team has prepared for Black Week? We’ve cut all the prices of our SQL courses. We also have something special for students. But hurry up, time is short! Black Week - Special Pricing: Individual SQL course - $25 Forever plan - $179 Forever plan for Students - $90 We know just how much you love to bag great discounts. SQL Black Week 2020 is on!

SQL JOIN Types Explained

What’s the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN in SQL? When should you use each one? We’ve got your answers right here. You want to combine data from two or more different tables, but you’re not sure how to do it in SQL. No worries. In this article, I will show you how to use the SQL JOIN clause to merge data from two tables.

How to Join Two Tables in SQL

Querying data from multiple tables is very common when working with relational databases. It is not difficult if you know how to use the dedicated SQL operators for doing this. In this article, you will learn how to join two tables by using WHERE and by using a special operator JOIN, and you will see how to filter rows in the result set. How to Query a Single Table First, a quick refresher on how to select data from a single table.

How to Practice SQL JOINs

There is no better way to learn SQL joins than through practice. However, there will probably be obstacles along the way. I’ll cover some of these obstacles and give ideas for how to overcome them. While this article won’t turn you into SQL JOINs expert, it will show you how to become one. So, let’s start! Challenges When Practicing SQL JOINs It’s hard to answer “How do you master SQL JOINs?

Converting Subqueries to Joins

Not all queries are alike, especially in terms of performance. In this article, we'll look at how you can convert SQL subqueries to joins for improved efficiency. When should I use SQL subqueries? Great question! Unfortunately, there's no concrete answer. SQL beginners tend to overuse subqueries. Typically, once they find that SQL construction works in one situation, they try to apply that same approach to other situations. It's only natural.

SQL Hacks To Control Family Budget On Black Friday Weekend

If you’re in the US, chances are you’ve been eagerly awaiting the approach of Black Friday just as much as Thanksgiving. Though the shopping frenzy takes hold of nearly everyone, some people have to stick to their budgets and shop prudently. In this article, we’ll take a look at how generating an SQL report can help you track how much your family spent shopping on Black Friday. Storing Black Friday Purchases in a Database Before we can create an SQL report, we first need some data we can use.

An Illustrated Guide to Multiple Join

So far, our articles in the "An Illustrated Guide" series have explained several join types: INNER JOINs, OUTER JOINs (LEFT JOIN, RIGHT JOIN, FULL JOIN), CROSS JOIN, self-join and non-equi join. In this final article of the series, we show you how to create SQL queries that match data from multiple tables using one or more join types. Join Types in SQL Queries Before we start discussing example SQL queries that use multiple join types, let's do a short recap of the join types we've covered so far, just to be sure you understand the differences.

An Illustrated Guide to the SQL Non Equi Join

Did you know that in SQL, a join doesn’t have to be based on identical matches? In this post, we look at the SQL non equi join, which uses ‘non-equal’ operators to match records. We’ve already discussed several types of joins, including self joins and CROSS JOIN, INNER JOIN and OUTER JOIN. These types of joins typically appear with the equals sign (=). However, some joins use conditions other than the equals (=) sign.

An Illustrated Guide to the SQL Self Join

What is an SQL self join and how does it work? When should it be used? We’ll provide answers to those questions! In SQL, we can combine data from multiple tables by using a JOIN operator. JOIN has several variants; we’ve already discussed CROSS JOIN, INNER JOIN, and OUTER JOIN. Most of the time, these operators join data from two or more different tables. You can practice all the different types of JOINs in our interactive SQL JOINs course.

How to Track Down Duplicate Values in a Table

When it comes to information management, duplicates present one of the most common challenges to data quality. In this article, I'll explain how it is possible to find and distinguish duplicate names with the help of the SQL data programming language. I really like my maiden name. The reason I like it so much is because it's rare. My maiden name (first with last) provided a unique identifier on platforms such as LinkedIn, Facebook, Twitter and similar.

An Illustrated Guide to the SQL OUTER JOIN

We’ve already discussed the SQL CROSS JOIN and INNER JOIN statements. It’s time to explore another: OUTER JOIN. What is it? How does it work? Let’s find out! If you’ve read our other posts, you know that you can link the data in two or more database tables using one of the many types of SQL join operator. Today, we’ll discuss the three kinds of OUTER JOIN: LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN.

An Illustrated Guide to the SQL INNER JOIN

What is an SQL INNER JOIN, and how does it work? Let's find out! In my last article, I discussed the CROSS JOIN operation in SQL. Today, we'll look at INNER JOIN and how to use it. Is it the same as a JOIN? How many tables can you link with an INNER JOIN? These are all good questions. Let's look at the answers! What is an INNER JOIN?

An Illustrated Guide to the SQL CROSS JOIN

What is an SQL CROSS JOIN statement? When should you use it? When shouldn't you use it? This post will tell you what you need to know about CROSS JOIN. You already know that you can use the SQL JOIN statement to join one or more tables that share a matching record. And if you're read the LearnSQL's post Learning SQL JOINs Using Real Life Situations, you know that there are many types of JOINs.

An Introduction to Using SQL Aggregate Functions with JOINs

Previously, we've discussed the use of SQL aggregate functions with the GROUP BY statement. Regular readers of the our blog will also remember our recent tutorial about JOINs. If you're a bit rusty on either subject, I encourage you to review them before continuing this article. That's because we will dig further into aggregate functions by pairing them with JOINs. This duo unleashes the full possibilities of SQL aggregate functions and allows us to perform computations on multiple tables in a single query.

Learning JOINs With Real World SQL Examples

The JOIN statement lets you work with data stored in multiple tables. In this article, I’ll walk you through the topic of JOIN clauses using real world SQL examples. Imagine if you could only work with one database table at a time. Fortunately, this isn’t anything we have to worry about. Once you learn the JOIN statement, you can start linking data together. In this article, I’ll use real world SQL examples that illustrate how we use JOINs, how each type of JOIN works, and when to use each type.

SQL JOINs

A SQL JOIN is a method to retrieve data from two or more database tables. This article presents a basic overview of what data from a particular SQL join will look like. A popular way of understanding SQL joins is to visualize them using Venn diagrams, so each example have corresponding Venn diagram, appropriate SELECT statement and the result table. There are a few major kinds of SQL joins:

SQL JOINs for Beginners

You’re probably already familiar with simple SQL queries, such as SELECT * FROM table. Now you are wondering what to do when you have multiple tables, and you want to join them. Exactly! JOIN is the key. In this SQL JOINs tutorial for beginners, you will learn how to connect data from multiple tables. What are SQL JOINs? Databases usually have more than one table. JOINs are an SQL construction used to join data from two or more tables.

Tag: Joins

What Is a Self Join in SQL? An Explanation With Seven Examples

The self join is a popular special case of the SQL JOIN. While most JOINs link two or more tables with each other to present their data together, a self join links a table to itself. This is usually done by joining a table to itself just once within a SQL query, but it is possible to do so multiple times within the same query. Typically, each table in a database stores a specific type of information.

How to Join the Same Table Twice

JOIN is one of the most common statements in SQL. As you may know, it is used to join and combine data from two or more tables into one common data set. In this article, I’m going to discuss special types of joins? in which you combine the same table twice—including joining a table to itself, also known as the self join. When and why do you need to do this?

SQL JOIN Cheat Sheet

Download this 2-page SQL JOIN Cheat Sheet in PDF or PNG format, print it out, and stick to your desk. The SQL JOIN Cheat Sheet provides you with the syntax of different JOINs, and examples. You can download this cheat sheet as follows: Download 2-page SQL JOIN Cheat Sheet in PDF format (A4) Download 2-page SQL JOIN Cheat Sheet in PDF format (Letter) Download 1-page SQL JOIN Cheat Sheet in PDF format (A3) Download 1-page SQL JOIN Cheat Sheet in PDF format (Ledger) SQL JOINs Cheat Sheet JOINING TABLES JOIN combines data from two tables.

Can you Join two Tables Without a Common Column?

Yes, you can! The longer answer is yes, there are a few ways to combine two tables without a common column, including CROSS JOIN (Cartesian product) and UNION. The latter is technically not a join but can be handy for merging tables in SQL. In this article, I’ll guide you through the different solutions with examples. When Do you Need to Join Tables Without a Common Column? Beginners just getting started with SQL are usually introduced to standard equi joins, in which two tables are combined by a common column.

What's the Difference Between Having Multiple Tables in FROM and Using JOIN?

What’s your approach to joining tables in SQL? In this article, we discuss two approaches and explain why many SQL developers have a definite preference for JOIN. Do you prefer to list multiple tables in FROM and use WHERE to set the join conditions? Or do you use the JOIN keyword? SQL supports both, but there are significant differences between them. Let’s look at each one in detail and then discuss why JOIN is generally preferred.

Practical Examples of When to Use Non-Equi JOINs in SQL

If you think that two tables in SQL can be joined only using the common field, you will be excited to learn that there are other ways of joining. Non-equi JOINs use different kinds of comparison operators in the JOIN condition. In this article, I’ll guide you through non-equi JOIN examples to show the common use cases for this type of JOIN. Equi JOIN vs. Non-Equi JOIN How do you usually join two tables in SQL?

How to Learn SQL JOINs

JOINs are one of the most fundamental and commonly used SQL commands for manipulating and querying real-world data sets. They are also one of the more challenging SQL topics to master! In this article, you’ll learn an effective strategy to learn the different types of SQL JOINs. When data is stored in a single table, we can easily retrieve rows and get all the information we need. But when businesses scale, so does their data.

Subquery vs. JOIN

One of the challenges in writing SQL queries is choosing whether to use a subquery or a JOIN. There are many situations in which a JOIN is the better solution, and there are others where a subquery is better. Let’s consider this topic in detail. Subqueries are used in complex SQL queries. Usually, there is a main outer query and one or more subqueries nested within the outer query.

How to Join 3 Tables (or More) in SQL

Using JOIN in SQL doesn’t mean you can only join two tables. You can join 3, 4, or even more! The possibilities are limitless. If you’ve just learnt JOINs in SQL, you might think that it’s limited to two tables. That’s not surprising – this concept can be hard to understand, and the idea that JOINs can get even more complicated may be really scary at first. The truth is that you can easily extend this idea to three tables or even more.

How to LEFT JOIN Multiple Tables in SQL

Can you LEFT JOIN three tables in SQL? Yes, indeed! You can use multiple LEFT JOINs in one query if needed for your analysis. In this article, I will go through some examples to demonstrate how to LEFT JOIN multiple tables in SQL and how to avoid some common pitfalls when doing so. What Is a LEFT JOIN? Let’s start by reminding ourselves what a LEFT JOIN is and how to use it.

Tag: Kurtosis

High Performance Statistical Queries –Skewness and Kurtosis

In descriptive statistics, the first four population moments include center, spread, skewness, and kurtosis or peakedness of a distribution. In this article, I am explaining the third and fourth population moments, the skewness and the kurtosis, and how to calculate them. Mean uses the values on the first degree in the calculation; therefore, it is the first population moment. Standard deviation uses the squared values and is therefore the second population moment.

Tag: Language

What Programming Language Should You Learn?

If you've ever been wondering which programming language you should learn first, you know that's a tough nut to crack. It’s especially difficult if you are new to IT and programming. In this article, I give suggestions for what to learn first and what perspectives each language can give you in IT. There are hundreds of programming languages, and new ones are showing up all the time. Getting to know all of them is simply impractical and impossible.

Tag: Learn sql

MS SQL Server vs. PostgreSQL: Which Should You Choose for a New Project?

Choosing the DBMS you will use for a new project is a very important and difficult decision. Two popular choices are MS SQL Server and PostgreSQL. To help you decide which would be best for you, I'll compare their features, list pros and cons, and give you some examples. Your selection of database management system (DBMS) depends on the type of business or project you're implementing. First, you need to know:

How Much SQL Practice Do You Need to Become a Pro?

Are you wondering how long it will take to learn and practice SQL before you can call yourself a pro? In this article, I will try to help you answer this question. Being a pro in SQL can mean many different things. Some people would say that being a professional is about mastery of advanced SQL, i.e. window functions or complex subqueries. For other people, being a professional means getting paid for your skills.

SQL Terms Beginners Should Know - Part 3

This is the third part of my list of essential SQL terms for beginners. In the first, you learned what tables, relational databases, and queries are. In the second part of the tutorial, I told you about aliases, SQL JOINs, primary keys, and subqueries. Now, it's time for more advanced database terms. But don't be afraid! I won’t crush you with scientific definitions. I will explain everything simply so that you can easily understand.

Use SQL to Filter Your Client Email Database & Organize a B2B SaaS Cross-Promotion

Looking for ways to be on friendly terms with your email database? Here's my way of using SQL to evaluate a promotion. A client database plays an essential role in developing your sales and marketing strategies. Having a clear and well-structured database has several benefits. For example, you can increase your company's revenue by managing your current and new clients – they can be monitored and offered special promotions. Moreover, such an effort develops customer satisfaction and increases value for your current customers.

Anniversary of LearnSQL.com

Consider the period from Feb. 23, 2020 to Feb. 22, 2021. A year, 255 working days. Is that a lot of time? Well, it depends. For the LearnSQL.com Team, the time has passed blazingly fast. If someone had told us a year ago that we would be where we are now, we would have said, ‘We wish!’. We had a clear vision and a plan to create the most comprehensive SQL training platform in the world, with the best set of hands-on online SQL courses, and top-notch reading materials.

Learn SQL And Start Your Journey Towards Personal Growth

Are you at the very beginning of your career and don't know what employers are looking for? Maybe you already have a lot of experience, but feel like it's time to change or update your skillset. Learning SQL can be a great choice. Read on and find out why. Regardless of your career stage, you cannot neglect your personal development. Whoever does not move forward falls behind. As you start learning new things, new opportunities will open up for you, both in your personal and professional life.

How to Practice PostgreSQL Online

PostgreSQL is hot right now!If you want to join a community of people passionate about data, this open-source database system is something you need to try. Like everything we teach on LearnSQL.com, PostgreSQL requires practice. To profit from Postgres – as this dialect is sometimes called – you need to start with the basics. You can watch some tutorials on YouTube or read articles to get to know what a Database Management System (DBMS) is.

What Is GROUP BY in SQL?

GROUP BY is a great SQL feature that allows you to perform powerful calculations on grouped data. Do you want to learn how to get powerful insights from your data? Would you like to know what GROUP BY does and when you should use it? If your answer is yes, keep reading. In this article, you will learn exactly that. Why You Need GROUP BY In today's digitized world – no matter what business you are in – database tables are usually huge, with millions of records.

Which SQL Books Should You Read in 2021?

Readers keep asking for books that I can recommend to complement our SQL courses. There are quite a lot of SQL books on the market, but only a few are worth your attention. See which SQL-related books to read in 2021. A while ago, I wrote an article about my favorite SQL books for 2020. I chose books about various aspects of working with databases with the goal of helping you get a clear picture of SQL in the real world.

Enumerate and Explain All the Basic Elements of an SQL Query

“What are the basic elements of an SQL query?” is a popular SQL job interview question. In this article, we review the basic syntax of an SQL query. An SQL query, which requests information from a relational database, consists of several elements. These allow you to select specific columns from specific tables and to filter and sort this information if necessary. In this article, I’ll briefly review these elements by explaining what each element does and how to use it.

Want to Learn Advanced PostgreSQL? Try This!

Why and how should you learn advanced PostgreSQL? I’ll give you some tips that will help you achieve your goals. Keeping up with technology is hard; anyone who has foolishly tried to do so can confirm this (me, for example!). Most of the time, it just doesn't work. And to be brutally honest, keeping up with all the technologies all the time is pointless. You shouldn’t know everything about everything; it’s better to know as much as you need within the technology you use or want to use.

What Does ORDER BY Do?

When analyzing data, it often helps to have rows ordered in a specific way. In this article, I’ll use multiple examples to show how SQL ORDER BY sorts data according to one or more columns in ascending or descending order. Introduction to ORDER BY By default, the order of rows in the output of an SQL query is arbitrary. If you want to sort the output in a particular order, you’ll need to use the ORDER BY keyword.

How to Import CSVs to PostgreSQL Using PgAdmin

Do you work with data and use CSV files? Here is a practical guide on how to import such files into a PostgreSQL database using pgAdmin, one of the best PostgreSQL editors on the market. Let's get right into importing CSVs into a Postgres database. We’ll start by explaining what a CSV file is, then we’ll introduce you to pgAdmin and show you how to do the import process. Don’t worry – it’s easy!

What Is a Unique Constraint in SQL?

To ensure the uniqueness of data in a database, we use the SQL UNIQUE constraint. In this article, we’ll discuss how, when, and why to implement it. The idea of a unique constraint is not unique to SQL; it’s a familiar concept in real life, although we probably call it something else! For example, think of ID numbers. There can be only one social security number (SSN) per person and each one must be unique.

How Much SQL Do I Need to Know?

Learning a new skill or starting a new profession can be a real challenge, especially when you’re unsure of how much you really need to know before taking the plunge. Imposter syndrome is also a real thing – how could you possibly catch up with all those SQL ‘experts’ who seem like they’ve been doing this since they were in diapers? The good news is you can learn SQL quickly and easily, and you don’t need to know nearly as much as you think you do.

SQL Course of the Month – SQL JOINs

If you want to really learn SQL, you can’t skip SQL JOINs. They are some of the most fundamental and commonly used features of the SQL language. That’s why SQL JOINs is our February SQL Course of the Month. What makes SQL JOINs so important? I asked Agnieszka Kozubek-Krycuń, Vertabelo's Chief Content Officer, about it. Here's what she said. Is it true that SQL JOINs are one of the foundations of SQL?

Data Types in SQL

Read this article and learn the ABC of SQL data types. Data types are used to define the type of data stored in a database. However, there are related concepts that a good SQL developer should know: data type conversion, what operations are possible between different data types, date arithmetic, etc. SQL also provides functions that manipulate values of different data types (i.e. functions for string data, date and time data, etc.

Using AND, OR, and NOT Operators in SQL

AND, OR, and NOT are important logical operators in SQL. They help you combine the conditions used to filter records. They are most commonly used in conjunction with the WHERE or HAVING clauses. Furthermore, this topic is a pretty common SQL job interview question. To help you completely understand these operators, I’ll take you through some examples, fully explaining the syntax and purpose of each. Practicing using examples like these is one of the best methods for learning SQL.

Why Aren’t SQL Window Functions Allowed in GROUP BY?

It’s true – the SQL order of operations means window functions aren’t allowed in GROUP BY. But you can use them anyway with this special trick. SQL window functions are one of the language’s most powerful features. However, the syntax of window functions is not easy to master. It has lots of details that can cause beginners to stumble. One of the most common traps is trying to use window functions in GROUP BY.

7 Common GROUP BY Errors

Are you making these errors with GROUP BY in SQL? Find out what they are, how to avoid them, and how to fix them. SQL’s GROUP BY statement can quickly uncover powerful data insights. At first, using GROUP BY can seem easy – e.g. when creating basic SQL reports that you’ll present to business decision-makers. But while learning this powerful feature, you could become trapped in weird errors or get incorrect results caused by improperly written GROUP BY statements.

Why Learn SQL Window Functions in 2021?

SQL window functions provide some extremely powerful and convenient features for data practitioners. This article explains why you should learn window functions and when you should use them. I’ll also provide some examples to help you visualize the concepts. Window functions are part of advanced modern SQL – knowledge of which will definitely enrich the repertoire of any SQL user. Window functions have a broad range of uses and can be applied to almost all facets of business.

Where Can I Find Good SQL CTE Exercises?

Find the top online resources for SQL Common Table Expression (CTE) exercises! CTEs allow you to structure and organize SQL queries efficiently, which is essential if you want to advance your SQL knowledge. A Common Table Expression, or CTE, is a SQL syntax that creates a temporary data set. This set contains separate data than the main query, which can typically be referenced or reused in a subsequent query. A CTE is considered temporary because the result is not permanently stored anywhere and only exists for the duration of the query.

Stories of the LearnSQL Scholarship Program

2020 is behind us. It was an extremely difficult year: We’ve struggled with the Covid-19 pandemic, a worldwide economic crisis, and constant anxiety. Many people have lost their jobs and their prospects for a better tomorrow. That's why we decided to do something positive: establishing a SQL scholarship program. We decided to find people in difficult situations and try to help them. For many, learning SQL can be their chance to get a job and develop their career.

What Is the SQL WHERE Clause?

The WHERE clause is a fundamental part of SQL. This clause filters results and applies conditions to SQL queries. It is most commonly used alongside the SELECT statement. If you’re a complete newcomer to this topic, you can learn the basics of SQL, including WHERE, in our SQL Basics course This article will clearly explain how to use WHERE in a SQL query. After reading it, you’ll have the confidence and knowledge to integrate WHERE into your daily work.

Monthly SQL Challenges in 2021

Did you know that LearnSQL.com provides a monthly SQL Challenge? Every month, we publish a new set of SQL practice exercises. Find out what to expect from our SQL challenges in 2021. Here at LearnSQL.com, we believe that the best way to learn SQL is through practice. After all, writing SQL is a practical skill. That’s why all our SQL courses (and there are over 30 of them!) are interactive: You learn SQL by writing SQL code.

What’s the Difference Between SQL CTEs and Views?

SQL views vs. CTEs: What do they do? How are they different? Which one should you use and when? Get your answers here! In SQL, both CTEs (common table expressions) and views help organize your queries, leading to cleaner and easier-to-follow code. However, there are some important differences between them. This article will walk you through several examples of CTEs and views and explain when to use each one.

What Is LEFT JOIN in SQL?

Get to know the details of LEFT JOIN, one of the most common SQL JOIN types. SQL is mainly about getting data from databases. Very often, you’ll need data to be combined from multiple tables in your database. That’s when JOINs come into play. LEFT JOIN is one of the JOIN types that you are likely to use very often. In this article, I’ll explain the syntax of LEFT JOIN and how it works using several examples and illustrations.

Best SQL Video Tutorials for 2021

Ready for this year’s picks for the best YouTube SQL video tutorials? Here are our top 5 choices! It's been well over a year since I last wrote about SQL tutorials on YouTube. Those seven channels can help you learn the basics of SQL quite painlessly, but now it's time to add to that list with 2021’s top contenders. Which YouTube SQL tutorials are worth your time and attention? I’ve got my favorites, but first, let’s consider an important question:

What Is Auto-Increment in SQL?

In this article, we’ll learn the basics of the auto-increment feature of SQL: what it is and how to use it efficiently. One of the many features offered by SQL is auto-increment. It allows us to automatically generate values in a numeric column upon row insertion. You could think of it as an automatically supplied default value – the next number in a number sequence – that’s generated when the row is inserted.

An Overview of Aggregate Functions in SQL

Aggregate functions are commonly used in SQL. This article will lead you through their use and show examples of how they work. SQL aggregate functions are a useful tool, especially for creating reports. They’re not difficult to understand, especially if you have some experience with Excel or similar programs. You’ve probably used aggregate functions like SUM or AVERAGE in a spreadsheet. Even if you only occasionally use them, knowing aggregate functions can help you better understand your data and work more efficiently.

LearnSQL Track of the Season: Creating Database Structure

New year, new challenges, and ... a new SQL Track of the Season! Start 2021 by learning SQL and data engineering. In this article, we answer frequently asked questions about our Creating Database Structure track. Maybe you haven't noticed yet that there’s an order to many LearnSQL.com courses; you can learn SQL by doing them in the right order. We call this option our ‘SQL tracks’. These are logically structured and well-thought-out learning paths that will help you take the next steps towards becoming an SQL expert.

SQL Course of the Month – Standard SQL Functions

Are you dreaming of becoming a data analyst? Or maybe you just want to work effectively with your company’s databases? You can – with SQL functions. We’ve selected Standard SQL Functions to be our January 2021 SQL Course of the Month. What will you find inside? I asked Agnieszka Kozubek-Krycuń, Vertabelo's Chief Content Officer, about it. Here's what she said. What are SQL functions? The term reminds me of SELECT or JOIN.

SQL JOIN Tips for Beginners

If you’re a beginner and want to know how to start using SQL JOINs in your queries, you’ve come to the right place. Using the SQL JOIN clause is necessary if you want to query multiple tables. Sooner or later, you’ll have to use more than one table in a query. It’s the nature of relational databases in general – they consist of data that’s usually saved in multiple tables; in turn, these form a database.

Why Should Learning SQL be One of Your New Year's Resolutions?

In answering this question, we’ll take a look at the idea behind New Year’s resolutions, explore what SQL is, and see why learning it should be your goal for 2021. We’ve all heard of New Year’s resolutions, and we all have personal experience of how difficult it can be to see them through to a successful conclusion. We’ll examine the history of New Year’s resolutions, why they often fail, and how to ensure your resolution for learning SQL in 2021 doesn’t meet with the same fate as so many others that never made it past the end of January.

2020’s Best LearnSQL.com Articles

We published a whole lot of interesting SQL articles this year. I had a difficult task – choosing the best LearnSQL.com articles of 2020. And here they are. The crazy year of 2020 is coming to an end. How will we remember it? Probably by the COVID-19 pandemic; we stayed home and fought the virus. It was a difficult time. However, many of us did not give up and kept trying to achieve our professional goals.

What Is a Database Index?

Database indexes are critical to query speed and efficiency. Learn when, why, and how to use them – and when not to – in this post. Indexes are very important database objects; they optimize data access and improve database performance by helping the database execute SQL queries faster. Why not take this opportunity to learn how indexes work and how to create them? What Is a Database Index? Indexes are data structures that can increase a database’s efficiency in accessing tables.

How to Practice SQL with LearnSQL.com

Practicing new skills online needs motivation and self-discipline, but it’s worth it. We’re facing a difficult, uncertain time. On one hand, the COVID pandemic caused a lot of fear. What will happen in the future? Will I keep my job? Will we stay safe and healthy? On the other hand, COVID is giving us a lot of time. Working remotely, not having anything to do but stay home and… And what?

What Is an SQL INNER JOIN?

How do you combine data from different tables in one query? An SQL feature called JOIN is the most common operator used to create complex queries. Learn the basics in this article. SQL allows us to select data from more than one table. In fact, the whole idea of using relational databases is selecting data from related tables. And we can use SQL’s JOIN operator to do this. There are many types of JOINs in SQL.

How SQL Window Functions Can Help Managers Decide Who Gets a Raise

Window functions are one of the most powerful features in modern SQL. In this article, you will learn why window functions are so great. I will list you the most useful window functions and briefly explain when and how you can use them. Simple SELECT statements, in combination with WHERE, GROUP BY, and HAVING, are sufficient for many analyses at work. I used standard SQL for many years before I realized there is something more.

The Best SQL Lectures on YouTube

YouTube contains a vast amount of information. The trick is to know how to find what’s valuable. If you type “SQL lectures” in the YouTube search engine, you will probably get a list of boring or unhelpful clips. However, there are hidden gems, and I’ve compiled a list of the best SQL talks I’ve found on YouTube so far. First, let's establish one thing. I didn't choose any YouTube SQL tutorials when making this list.

Best Online Courses for SQL Window Functions

In this article, I will summarize the top online tutorials and courses available on SQL window functions for enthusiasts of data analysis, data science, and data engineering. The information is here to help you embrace the topic with ease and feel comfortable using window functions in SQL databases. SQL window functions can help you solve some of the most common analysis challenges in business: What are the N most popular products for each month of the year?

How to Use CASE WHEN With SUM() in SQL

This article will teach you what a CASE WHEN expression is in SQL and how to use it with a SUM() function and a GROUP BY statement. The examples are included to bolster your understanding. Knowing how to use a CASE WHEN expression in SQL adds insight into the exciting possibilities in SQL. It elevates you from a simple user who depends on what SQL returns, to a user who is more in command and who sets specific criteria in SQL.

SQL Scholarship Program 2020

2020 is slowly coming to an end. It was extremely difficult for everyone. We’ve therefore decided to end it with something positive. This Holiday, we want to help someone change their life. Learn SQL will fund 50 SQL Scholarships for people who cannot afford to learn SQL and who may find it helpful in a difficult situation. We’ll hand out our flagship track - SQL From A to Z - for FREE!

What is an SQL View?

A view is a well-known feature in SQL. It allows you to create a virtual table based on an SQL query referring to other tables in the database. A view stores an SQL query that is executed whenever you refer to the view. This is a convenient way to get the desired data because it is easier to run a query stored in a view than to type a query from scratch.

Practicing SQL for Your First Day of Work

Your new SQL job is likely to surprise you in many ways. To minimize the risk of getting lost in the jungle of data, I recommend you get some additional SQL practice before your first day. There are special SQL practice sets and projects on the internet to help you prepare. You’ll also get help from your colleagues, as programmers are usually open and supportive. If you’re reading this, you’ve probably heard about the opportunities SQL and data science offer.

The Top 10 SQL JOIN Interview Questions and How to Answer Them

Have you ever wondered what SQL JOIN questions you might be asked in an interview? Do you feel prepared to answer them? This article covers the most common SQL JOIN interview questions and how to answer them. If you are applying for a job as a data analyst or software developer, you will likely be asked about your SQL JOIN knowledge. SQL JOIN clauses are a great topic for interviewers to quiz you on.

The History of SQL Standards

Has the SQL standard changed in the 30+ years it's been around? Absolutely! Learn about the journey from SQL-86 to modern SQL, today’s standard data language. SQL was created in the early 1970s by IBM. In 1974, Donald Chamberlin and Raymond Boyce published the article SEQUEL: A Structured English Query Language, which introduced SQL to the world. The article contained the BNF grammar (a detailed technical description of the language syntax) for the language, which IBM later thought was a mistake.

SQL Terms Beginners Should Know – Part 2

This is the second part of my list of essential SQL terms for beginners. In the first, you learned what a table, relational database, and query are. Now, it's time for more advanced database terms. But don't be afraid! I won’t crush you with scientific definitions. I will explain everything simply so that you can easily understand. If you want to review the basic SQL terms, see my previous article, SQL Terms Beginners Should Know.

How Do You Write a SELECT Statement in SQL?

SQL is a language to communicate with relational databases, and the SELECT statement is the first thing you’ll learn when you start using SQL. In this article, you’ll learn how to write SELECT statements, from the basics to more advanced. What Is SQL? SQL stands for “Structured Query Language.” It has a long history that started in the 1970s. Being the standard for communication with relational databases, it has maintained its popularity.

SQL Technologies Are More Common Than You Think

Where is SQL being used today? The answers might surprise you! (Hint: SQL technology is basically everywhere.) Is it worth learning SQL? After all, the language was created in the 1970s. Is it still relevant today? The list of technologies that support SQL is very long – and it’s growing. Read on to find out what kinds of programs use SQL. SQL in Databases Relational Databases = SQL Databases It’s no surprise that SQL is used in relational databases.

SQL Course of the Month – Customer Behavior Analysis in SQL

Do you run a business? Do you want to squeeze even more out of your data? Start by analyzing your customers' behavior using SQL! Throughout December, you can learn how to do it for free on LearnSQL.com! I asked Agnieszka Kozubek-Krycuń, Vertabelo's Chief Content Officer, about our December Course of the Month, Customer Behavior Analysis in SQL. Here's what she told me. Let's start with the basics: Why analyze customer behavior?

What Is a Foreign Key in SQL?

What does a foreign key do in SQL? Why would you need one? Learn the ABCs of foreign keys in five minutes. Foreign keys are a central concept in SQL databases; they allow us to enforce data consistency. Usually they work with primary keys to connect two database tables, like a virtual bridge. All SQL developers need to know what SQL foreign keys are, how they work, what data values are allowed in them, and how they’re created.

SQL Window Functions vs. SQL Aggregate Functions: Similarities and Differences

If you aren’t familiar with SQL’s window functions, you may wonder how they differ from aggregate functions. When should you use window functions? In this article, we’ll review window functions and aggregate functions, examine their similarities and differences, and see which one to choose depending on what you need to do. After you’ve tackled basic SQL, you’ll probably want to get into some of its more advanced functions. That’s great; these functions make reporting and analysis easier.

How to Find All Employees Under Each Manager in SQL

Have you ever been tasked with building an organizational chart – i.e. finding the employees under each manager in a company? In SQL, you can do that easier than you think! This article will show you how to get the answer using a recursive query. In the business world, it’s a very common task to list all the subordinate employees for a given manager. Is doing this hard enough to warrant a whole article?

SQL in the Open-Source World

Did you know there are free, open-source databases that use SQL? In this article, I'll show you which open-source database solutions can meet your needs. Ever wonder why many people still use paid programs when the same things can be done with free options? Personally, I am an avid supporter of the open-source movement. For years, I have been trying to apply and promote such solutions and support an active community around them.

SQL Black Week 2020. See how much you can save!

Wow, have you seen what discounts the LearnSQL.com Team has prepared for Black Week? We’ve cut all the prices of our SQL courses. We also have something special for students. But hurry up, time is short! Black Week - Special Pricing: Individual SQL course - $25 Forever plan - $179 Forever plan for Students - $90 We know just how much you love to bag great discounts. SQL Black Week 2020 is on!

How To Learn The SELECT Statement in SQL

When you think about learning SQL, one of the first things you come across is the SELECT statement. Selecting information is arguably the most important SQL feature. In this article, we’ll demonstrate the typical use cases for SQL SELECT with practical examples. Read this article if you’re a beginner database user and would like to know what SELECT can do for you. SQL, or Structured Query Language, is the programming language the IT world uses to communicate with databases.

What Is a SQL Constraint?

What are SQL constraints? When and why should you use them? We give examples of common constraints and demonstrate how to apply them. When you’re creating a relational database, you often want to impose certain restrictions on some columns. For example, a column containing a social security number should store only unique values; a column containing a date of birth should not be null, or left empty. These conditions can be ensured by using SQL constraints.

The History of SQL – How It All Began

Who created SQL and why? Find out in this article! Are you learning SQL? Or are you about to take the first step towards working with databases? Great decision! Either way, it's worth knowing the history of SQL – where it came from, who came up with it, and why. Here’s a brief history of SQL, starting with its foundational concept: the database. Ted Codd and the Relational Data Model The first computer databases appeared in the late 1960s.

Practice SQL Before Interviewing a Potential Employee

Has your company grown to the point that you need to hire an SQL expert? Have you found a candidate for the job? How do you prepare for the interview, especially if you don’t know SQL? Don't worry! Follow our suggestions on how to practice SQL. We have tips and tricks to help you feel confident and find the perfect employee. Who You Want To Hire First of all, you need to know the requirements for the new employee.

SQL JOIN Types Explained

What’s the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN in SQL? When should you use each one? We’ve got your answers right here. You want to combine data from two or more different tables, but you’re not sure how to do it in SQL. No worries. In this article, I will show you how to use the SQL JOIN clause to merge data from two tables.

Top 7 Online Courses for Data Engineers

This article summarizes the top online courses available for data engineers. We have picks suitable for beginners as well as intermediate learners. If you’re interested in database design and management, check these courses out! Most individuals who aspire to enter the realm of data aim for data scientist or data analyst roles. While these roles are indeed very rewarding because of their tangible links to customers and business direction, the role of data engineers is equally vital for businesses that operate in a data-rich environment.

SQL Terms Beginners Should Know

Have you started learning SQL? Do you feel a little lost in the maze of new words and ideas? Here’s a list of 10 absolutely essential SQL terms for beginners. When you start learning SQL, there’s a lot to process. And some of it – even basic SQL terms – gets lost in the shuffle. If this sounds like you, bookmark this article; it will be a handy reference.

Where to Go After Learning SQL Basics

Learning to code is – in general – a lot of fun, for sure. Even after a few years in the IT industry, I still love learning new technologies. And I now know that learning with a good plan is even better than learning without one. This also applies to learning with advanced SQL courses. In this article, I'll show you how learning paths can save you some time and a lot of frustration.

Don't Be a SQL Noob! Start Learning with Our SQL Basics Course

Why learn SQL from our interactive online courses? Two reasons: 1) Power up your career. 2) Avoid being a noob. What does it mean to be a noob? “Noob” comes to us from the world of computer games. It’s a combination of “newbie” and “beginner”. It’s not a very nice word. It means that someone has found you an inexperienced player and (even worse) resistant to learning. This resistance is what’s important.

SQL Course of the Month – GROUP BY Extensions in SQL

Do you want to develop your SQL skills? Do you want to get more out of your data and prepare better reports and summaries? The answer is learning to use SQL’s GROUP BY extensions. But how should you go about this? I asked the same question to Agnieszka Kozubek-Krycuń, Vertabelo’s Chief Content Officer. As she explains, the secret is in this November’s free SQL Course of the Month: GROUP BY Extensions in SQL.

What is the Difference Between COUNT(*), COUNT(1), COUNT(column name), and COUNT(DISTINCT column name)?

Have you noticed there are different variations of the SQL COUNT() function? This article explains the various arguments and their uses. As a SQL user, you’re probably quite familiar with the COUNT() function. Even though it’s relatively simple, it can be used in several different ways. Each way has a very different use. I imagine you’ve seen code that contains the function COUNT(*) or COUNT(1). You’ve probably also seen some other uses of the COUNT() function, such as COUNT(column name) and COUNT(DISTINCT column name), even if you haven’t used them.

What are SQL CTE Best Practices?

Are you wondering what the best practices for using common table expressions are? This article will help you learn when to use a CTE and how to write it. If you have heard about SQL CTEs, you have probably noticed they’re often mentioned together with subqueries. Sometimes, people think there’s no difference compared to the subqueries, and there’s often debate about whether a CTE or subquery should be used to get a particular result.

How to Fix a 'Not a GROUP BY Expression' Error

Whether you are an experienced SQL user or only a beginner, your SQL queries may return errors. The accompanying messages are supposed to help you fix them; however, sometimes the messages are not very helpful. The Oracle message “Not a GROUP BY expression” is one such example. Let’s review what this is about and how to fix it. We are going to assume some basic understanding of how GROUP BY works.

Haunted Halloween Promotion - Join the Scavenger Hunt!

Trick or treat! Halloween, the festival of monsters is approaching! The LearnSQL platform is overrun by ghosts. They have haunted our courses. Are you scared, do you feel chills? We are most concerned about the prices. It’s highly probable the wraights will bite them off. But to quote the classics - “Who ya gonna call? Ghostbusters!” So put on the costume, take the astral trap and find them all to win our scavenger hunt.

How to Learn SQL Common Table Expressions (CTEs)

Common table expressions are very useful for organizing, traversing, and improving the readability of long SQL queries.  Moreover, recursive CTEs, which can reference themselves, solve problems that cannot be addressed with other queries. But how do you master common table expressions in SQL? In this article, I discuss the most effective strategies for learning CTEs and suggest how to address the common challenges of learning common table expressions on your own.

What is a Primary Key in SQL?

Primary keys are an important concept in SQL databases. They provide a unique ID for every row in a database table. As an SQL developer, you should know what primary keys are, what data values are allowed in them, and how to create them. Read this article to learn the ABCs of primary keys in 10 minutes. How to Identify Rows in a Table Tables are the main objects in an SQL database, and as you probably know, tables store records or rows.

Learning SQL for Free – Is It Worth Betting on Free Online Learning?

Everyone likes to get something for free, even when it comes to SQL courses. But is free always good? Find out how and where you can learn SQL for free – in a way that’s worth your time. Beginner-friendly database courses and SQL tutorials often promise to teach SQL fundamentals like SELECT, WHERE, GROUP BY, HAVING, and ORDER BY. These commands are the basis of a powerful set of skills for entry-level jobs in data analysis or databases.

What Is a DBMS?

We generate vast quantities every day, and that data needs to be stored somehow. That’s where DBMSs come in handy. Find out what they are and how they relate to databases. If you go on a diet and simply want to keep track of your weight, you can probably use a piece of paper and a pencil. If you then want to chart your daily caloric intake, you’ll probably switch to something like a computer spreadsheet.

Google Analytics and SQL

Google Analytics is a very popular tool among website and blog owners alike. With a simple and quick setup, it lets you gather data about your web page visitors easily. However, did you know that you can export data from Google Analytics to create your own SQL reports? Read this article to find out how. Google Analytics is an extremely popular and powerful solution that lets you collect and analyze various kinds of information about your website.

How to Boost Your Company With SQL Courses

SQL has the power to supercharge the capabilities and performance of your entire company. But if you don’t dip your toes in the water and give some SQL courses a go, you’ll never realize the vast potential of the language. SQL, or Structured Query Language, is your ticket to expanding the scope and the results of your business or organization, no matter what sector you operate in. Whether you’re the owner or manager of your company or simply an employee interested in improving operations, learning SQL is undoubtedly, unquestionably, for you.

SQL HAVING Tutorial

Learn how to use the SQL HAVING clause to filter groups using your own specified conditions. The SQL HAVING clause is often a challenging concept to grasp, especially for beginners. Additionally, its specific use cases can be difficult to visualize without specific examples based on real-world datasets. In this tutorial, you will learn how to apply the SQL HAVING clause to filter groups of records based on specified conditions. You’ll see examples where we apply this concept to solving business problems on a realistic dataset.

What Is a Self Join in SQL? An Explanation With Seven Examples

The self join is a popular special case of the SQL JOIN. While most JOINs link two or more tables with each other to present their data together, a self join links a table to itself. This is usually done by joining a table to itself just once within a SQL query, but it is possible to do so multiple times within the same query. Typically, each table in a database stores a specific type of information.

How to Join the Same Table Twice

JOIN is one of the most common statements in SQL. As you may know, it is used to join and combine data from two or more tables into one common data set. In this article, I’m going to discuss special types of joins? in which you combine the same table twice—including joining a table to itself, also known as the self join. When and why do you need to do this?

5 Best Online SQL Courses for Business Analysts

Why bother to learn via an online SQL course? SQL is pure profit – it allows analysts to interpret data efficiently and companies to adopt better strategies. In this post, we’ll look at our top 5 SQL courses for business analysts. Being into finance, economics, and IT systems has brought you to business analysis. It’s a fascinating combination of skills; you’re combining business and technology, which makes you a valuable asset to your company.

How to Create Your First Table in SQL

Creating a database table with SQL is one of the core skills you’ll need to work with data. And it’s easy to learn, so let’s get started! Imagine you’re analyzing data and want to store your results in a database table. Sure, you've done this a million times in Excel. But you’re not sure how to create a table with SQL. Or maybe you’ve noticed that data engineering is in high demand and you want to start learning its core concepts.

Five Essential Features of a Good SQL Course: What to Look for When Choosing a Course for You

There are many different platforms offering SQL courses. If you’re a beginner, it may be difficult to choose the right one for you. Find out what we think are the essential features of a good SQL course. Remember, if you make a poor choice at the beginning, you may get discouraged or get into bad habits that will impact your work down the line. What Is SQL? SQL, or Structured Query Language, is a programming language you use to talk to databases.

A Comprehensive Introduction to Window Functions in MySQL

Do a deep dive into the working principles, syntax, and applications of various MySQL window functions. There are many open source databases you could choose; MySQL is consistently one of the most popular. But until 2018, there was no provision for including window functions in MySQL. Fortunately, all that has changed – starting from MySQL 8.0, SQL window functions were now available to MySQL users. Please note that window functions are available only in MySQL 8.

SQL Course of the Month – How to INSERT, UPDATE, and DELETE Data in SQL

So, you've started learning SQL, and you already know what the SELECT command is and when to use it! Congratulations! Now, it's time to take the next step towards becoming an expert. You need to know the SQL UPDATE, INSERT, and DELETE commands to modify data in your tables. These are the basics that will allow you to work with tables. But what's the best way to learn them? I asked Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo.

How Will Learning SQL Make You a Better Boss?

Want to improve the performance of your team, of your own, of your department, or of your entire company? Try SQL! Why should you learn SQL? Because it just pays off! What does learning SQL and being a better boss have to do with each other? Being a better manager can make your employees happier while growing your business. When employees feel a sense of fulfillment, they are more motivated to do well.

Six Window Function Templates to Save in Your Code Editor

Do you use window functions often enough to know them well but not often enough to remember all the details? Here are six window function codes you should save as templates. Window functions are a handy SQL option, but it doesn’t mean you use them all the time. Maybe you only use them occasionally; if that’s the case, you probably find yourself needing to refresh your memory every time you use them.

New Course: Customer Behavior Analysis in SQL

Good news! A new SQL course is here! We’re happy to announce the release of our Customer Behavior Analysis in SQL course. Do you want to get to know your clients and better understand their needs and behavior? If so, this great interactive SQL course is for you. Discover the power of full customer lifecycle analytics in SQL and know more than your competitors. The LearnSQL.com team is happy to announce the release of a new SQL course on our platform: Customer Behavior Analysis in SQL.

SQL Courses in New York City

If someone asks me where to learn SQL, I answer simply: online! A good interactive SQL course is much better than any classroom activity or bootcamp. First, you do everything at your own pace. You can always ask the tutor about anything, be a part of an online community, and read interesting things elsewhere on the web (e.g. on our blog). However, there are those who prefer full-time courses. They are traditionalists.

What Is the MySQL OVER Clause?

If you want to learn window functions in MySQL, you need to understand the OVER clause. In this article, we use real-world examples to explain what the MySQL OVER clause is, how it works, and why it’s so awesome. In 2018, MySQL introduced a new feature: window functions, which are accessed via the OVER clause. Window functions are a super powerful resource available in almost all SQL databases. They perform a specific calculation (e.

SQL Means Business - The Way of an Engineer

Have you been wondering why some companies fail and others achieve success? It's not a matter of luck but of the right people. Łukasz Kubicki at Vertabelo deals with business and product development. I asked him how he started his adventure with programming, how an engineer got into business, and if he liked playing computer games. Here's what he said. If you were to write one sentence about yourself, what would it be?

Did You Know LearnSQL.com Has Free SQL Courses?

Who doesn't like getting something for free? Each month, we give LearnSQL.com users a bit of help in their learning journey – a free, fully interactive SQL course. Since April, we have been giving our users the opportunity to learn SQL for free. Each month, we choose one of our SQL courses and give you full access to it for that month – completely free of charge! Cool, right?

How Much Do Data Engineers Earn in 2020?

Data engineering is a hot job right now. What does a data engineer do? And just how much do they earn? We’ve done the research for you. If you are reading this, you’re either starting to learn SQL or you already know some and feel it’s time to look around for a SQL job. Maybe you’re in the midst of tackling our Creating Database Structure track. And, let’s be honest, maybe you need some extra motivation to keep on you track.

How to Use 2 CTEs in a Single SQL Query

Have you ever wondered how to use multiple CTEs in one SQL query? Read this article and find out about recursive CTEs. After learning common table expressions or CTEs, a natural question is “Can I use several CTEs in one query?” Yes, you can! And you can do it quite easily, especially if you already have some basic knowledge of CTEs. Whether you know a bit about CTEs or you’re entirely new to the CTE world, reading about what a CTE is is always a good start.

How to Join Two Tables in SQL

Querying data from multiple tables is very common when working with relational databases. It is not difficult if you know how to use the dedicated SQL operators for doing this. In this article, you will learn how to join two tables by using WHERE and by using a special operator JOIN, and you will see how to filter rows in the result set. How to Query a Single Table First, a quick refresher on how to select data from a single table.

GROUP BY in SQL Explained

The SQL GROUP BY statement is easy to use, but it can be hard to master. Learn what you can do with GROUP BY, how it works, and how to use it with aggregate functions. GROUP BY is one of the basic SQL tools. However, it might be difficult for beginners to understand how GROUP BY works and how it is used to compute statistics with different aggregate functions. In this article, I’ll use several examples to show exactly how GROUP BY organizes rows and how aggregate functions can be used to calculate statistics on one or more columns.

Top 5 Beginner Online SQL Courses in 2020

Looking for an exciting new career? Data analysis won’t disappoint you! The simplest way to make this possible is by learning SQL, and online SQL courses are the most effective learning method. Don’t know where to start? Here’s an overview of the best online SQL courses for complete beginners. There are infinite reasons for changing your industry. You may want to land a new job because you’re burnt out. You may be bored and want something more challenging.

Behind the Scenes at LearnSQL.com: How Our SQL Courses Are Created

Take a peek behind the scenes and learn our secret for creating great SQL courses! Have you ever wondered how LearnSQL.com courses are created? Are we looking at a lot of hard work or just a bit of magic? Or maybe both? Here’s a hint: we rely on proven methods to create user-friendly online courses. But it’s not easy! Read on to see the 8 steps we take when creating a new SQL course.

Why and How to Find Freelance SQL Jobs

If Covid-19 has you all “I-want-to-stop-working-for-the-man-and-enjoy-a-more-fulfilling-life-as-the-master-of-my-own-destiny”, then I’ve got news for you. Not only is it possible to be an SQL freelancer, it’s also a potentially lucrative and liberating career move. It will allow you to work for a diverse range of clients and march to the beat of your own drum. Of course, SQL freelancing isn’t for everyone. You will need a strong sense of self-motivation, some serious hustling skills, and the ability to sell yourself and your services as THE ABSOLUTE BEST all the time, every time - day in, day out.

Six Examples Using MySQL Window Functions

Window functions are an advanced SQL feature available in most popular databases. MySQL had not supported them for a long time, but that changed in Version 8.0. They are helpful not only for analysts and people who create reports, but also for other professionals who use databases to select data needed. In this article, we explain the syntax of some popular window functions with practical examples. What Is a Window Function?

What a Moving Average Is and How to Compute it in SQL

Want to dive deep into time series data and examine long-term trends? Want to know what a moving average is and how to compute it in SQL? Then this article is for you. I’ll explain a powerful feature in SQL called window functions and show how you can calculate moving averages using them. What Is a Moving Average? The moving average is a time series technique for analyzing and determining trends in data.

LearnSQL Track of the Season: SQL from A to Z

During Fall 2020, our main SQL track, SQL from A to Z, will be in the spotlight. In this article, we answer the most frequently asked questions about this track. At LearnSQL.com, our SQL courses are organized into tracks. A track is a sequence of courses designed to help you achieve a specific learning goal. The courses in the track are in a recommended order that progresses from the easiest to the most challenging.

How to Find Duplicate Values in SQL

Duplicate records waste time, space, and money. Learn how to find and fix duplicate values using SQL’s GROUP BY and HAVING clauses. Database best practices usually dictate having unique constraints (such as the primary key) on a table to prevent the duplication of rows when data is extracted and consolidated. However, you may find yourself working on a dataset with duplicate rows. This could be because of human error, an application bug, or uncleaned data that’s been extracted and merged from external sources, among other things.