How to Get Descendants of a Parent in SQL

by Tihomir Babic Want to learn how to handle family trees and find descendants of a parent? By reading this article, you’ll learn how to handle hierarchical data. Finding descendants from a parent is a common problem in SQL. If you imagine a family tree, the basic building block that forms the relationships within it is the parent-child relationship. The parent-child relationship is precisely what defines all hierarchical data. Another example of hierarchical data is the manager-employee relationship.

What Do the Operators LIKE and NOT LIKE Do?

by Andrew Bone The SQL LIKE and NOT LIKE operators are used to find matches between a string and a given pattern. They are part of standard SQL and work across all database types, making it essential knowledge for all SQL users. Gaining an understanding of these operators will allow you to write better queries and demonstrate to potential employers that you have the skills required to filter through expansive data sets.

How to JOIN Tables in SQL

by Kateryna Koidan Do you need to display data stored in different tables? Then it’s time to use SQL JOINs! This can be a challenging topic for beginners, so I’ve prepared this comprehensive step-by-step guide on joining tables in SQL. Often, the information that you want to display is stored in several tables. In such cases, you’ll need to join these tables by specifying which rows should be combined with other rows. That’s exactly what JOIN does.

Free SQL Course of the Month – Window Functions

by LearnSQL.com Team Are you looking for a good SQL window functions course? What if I told you that throughout March, you could access the best window functions course in the world for absolutely FREE? You read that right: you won't pay a dime! Hurry up! Time is running out! But wait – why is LearnSQL.com giving you a free SQL course? Well, we believe sometimes you just have to be good to others.

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

by Martyna Sławińska 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?

by Timothy Edison 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

by Jakub Romanowski 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

by Kate Stolarek 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

by LearnSQL.com Team 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

by Karolina Niewiarowska 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

by Kamila Ostrowska 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?

by Marija Ilic 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?

by Jakub Romanowski 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

by Kateryna Koidan “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!

by Tihomir Babic 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?

by Kateryna Koidan 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

by Jakub Romanowski 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?

by Martyna Sławińska 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?

by Rebecca McKeown 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

by LearnSQL.com Team 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

by Ignacio L. Bisso 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

by Andrew Bone 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?

by Agnieszka Kozubek-Krycuń 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

by Marija Ilic 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?

by Zahin Rahman 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?

by Zahin Rahman 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

by Jakub Romanowski 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?

by Andrew Bone 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.

What’s the Difference Between SQL CTEs and Views?

by Kateryna Koidan 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.

Monthly SQL Challenges in 2021

by Agnieszka Kozubek-Krycuń 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 Is LEFT JOIN in SQL?

by Kateryna Koidan 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

by Jakub Romanowski 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?

by Martyna Sławińska 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

by Tihomir Babic 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

by LearnSQL.com Team 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

by LearnSQL.com Team 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

by Tihomir Babic 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?

by LearnSQL.com Team 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

by Jakub Romanowski 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?

by Ignacio L. Bisso 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

by Kamila Ostrowska 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?

by Dorota Wdzięczna 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

by Marija Ilic 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

by Jakub Romanowski 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

by Zahin Rahman 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

by Tihomir Babic 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

by LearnSQL.com Team 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?

by Martyna Sławińska 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

by Arleta Więch 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

by Andrew Bone 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

by Agnieszka Kozubek-Krycuń 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

by Jakub Romanowski 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?

by Kateryna Koidan 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

by Agnieszka Kozubek-Krycuń 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

by LearnSQL.com Team 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?

by Ignacio L. Bisso 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

by Kateryna Koidan 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

by Tihomir Babic 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

by Jakub Romanowski 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!

by LearnSQL.com Team 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

by Adrian Więch 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?

by Martyna Sławińska 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

by Agnieszka Kozubek-Krycuń 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

by Kamila Ostrowska 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

by Marija Ilic 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

by Zahin Rahman 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

by Jakub Romanowski 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

by Magdalena Wojtas 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

by Jakub Romanowski 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

by LearnSQL.com Team 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)?

by Tihomir Babic 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?

by Tihomir Babic 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

by Kateryna Koidan 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!

by Jakub Romanowski 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)

by Kateryna Koidan 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?

by Ignacio L. Bisso 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?

by LearnSQL.com Team 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?

by Adrian Więch 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

by Adrian Więch 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

by Rebecca McKeown 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

by Zahin Rahman 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

by Martyna Sławińska 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

by Marija Ilic 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

by Marcin Koryszewski 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

by Marija Ilic 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

by Agnieszka Kozubek-Krycuń 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

by Martyna Sławińska 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

by LearnSQL.com Team 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?

by Kamila Ostrowska 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

by Tihomir Babic 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

by LearnSQL.com Team 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

by Jakub Romanowski 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?

by Ignacio L. Bisso 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

by Jakub Romanowski 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?

by Jakub Romanowski 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?

by Marcin Koryszewski 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

by Tihomir Babic 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

by Dorota Wdzięczna 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

by Kateryna Koidan 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

by Arleta Więch 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

by Agnieszka Kozubek-Krycuń 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

by Rebecca McKeown 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

by Dorota Wdzięczna 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

by Marija Ilic 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

by LearnSQL.com Team 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

by Zahin Rahman 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.

SQL Course of the Month – Analyzing Revenue Trends in SQL

by LearnSQL.com Team 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.

How CTEs Work

by Adrian Więch 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.

How Does SQL GROUP BY Work?

by Ignacio L. Bisso 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.

SQL CTEs Explained with Examples

by Kateryna Koidan 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.

How to Calculate the Length of a Series with SQL

by Tihomir Babic What is a time series and why bother to calculate its length using SQL? How do we calculate the length of a series in SQL? I can answer that in two words: window functions! Yes, you’ll need some knowledge of SQL window functions to calculate series length. But what is a time series, and why would you want to find out how long it is? What Is a Series?

Where Can I Find Free Online Data Sets to Practice SQL?

by Jakub Romanowski Okay, you've installed the RDBMS of your choice. You know the basics of SQL and ... what's next? You would like to be able to practice SQL functions you learned in our course. Maybe you have even done our SQL Practice Set course and are hungry for more. To work with a database, first of all, you need—yes, this is not a surprise—a database! Where do you get the data for your SQL queries?

5 Examples of GROUP BY

by Adrian Więch 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.

How to Create a Table in SQL

by Dorota Wdzięczna 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.

The Most Popular Databases in 2020

by Jakub Romanowski 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?

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

by Martyna Sławińska 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.

How to Spend Less by Mastering the Monthly Budget in SQL

by Adrian Więch Do you struggle to keep your budget under control? You must have heard about various budget planning materials available as printouts, Excel spreadsheets, or smartphone apps. In this article, we’ll show you another possibility. You’ll learn how to use databases and SQL to identify the weak points of your home budget and spend less. We all need to pay for everyday necessities such as groceries or medical appointments. With money coming in and out of our pockets, it’s easy to lose track of how much we spend and if we have any savings.

Is There any Demand for SQL Language Nowadays?

by Rebecca McKeown SQL is 46 years old. That’s 14 years older than I am, and at least 23 years older than the jar of pickles in my refrigerator. SQL is the still-hip granddaddy of the programming world. You know the one: non-ironic suspenders, twirled mustache, tattoo peeking out over his spotted socks. He may be old, but boy, is he fly. If you’ve heard of the NoSQL movement, you may be wondering: why learn SQL in this day and age?

5 Reasons You Might Fail to Learn SQL

by Kamila Ostrowska Learning SQL isn’t hard, but that doesn’t mean you’ll sail through, problem-free. Here are five things that might cause unwary SQL learners to fail. For me, learning SQL wasn’t always about the joy of discovery. Learning itself is not all about curiosity and the satisfaction of succeeding. Sometimes there is a sense of failure. We’re often told it is better to focus on positives. I believe this. However, it is also crucial to find out what went wrong when we don’t succeed at something.

Learning SQL When You Work and Have a Family

by Jakub Romanowski Do you want to learn SQL but feel you can’t squeeze one more thing into your jam-packed life? Here are my tips on learning SQL when you work and have kids. You work full-time and have a family. Daily responsibilities overwhelm you. I’ve been there. Heck, I live there. I work from home and have a family. While I was writing this article, I was also waiting for a call on Zoom, doing the laundry, and cooking some pasta for my son’s dinner.

Can you Join two Tables Without a Common Column?

by Kateryna Koidan 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.

Who Should Learn SQL Window Functions?

by Tihomir Babic Do you want to learn how SQL window functions can help you at your job? This article will show you examples from various business applications where they can be very useful. I won’t be explaining what SQL window functions are in this article, but rather how to use them. If you’re not familiar with window functions or their syntax, don’t worry. Here’s an article that can help you with an introduction to SQL window functions.

SQL Course of the Month – Recursive Queries

by LearnSQL.com Team 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.

The SQL HAVING Clause Explained

by Dorota Wdzięczna 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.

How to Use Subqueries in INSERT, UPDATE, and DELETE Statements

by Ignacio L. Bisso Did you know that subqueries can also be used in UPDATE, INSERT, and DELETE statements? Subqueries in SQL are like building blocks that can be used in a variety of statements, not just SELECT. If you find subqueries useful in SELECT, read this article to find out how useful they can be in other instructions. You will be able to create much more complex and powerful SQL queries in no time!

Our 6 Favorite SQL Books for 2020

by Jakub Romanowski 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?

Who Is a Data Engineer?

by Adrian Więch 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.

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

by Kateryna Koidan 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.

How to Analyze a Time Series in SQL

by Marija Ilic Values ordered by time are called a time series. In this article, I’ll show you the most frequent patterns and teach you how to write queries for time series in SQL with the help of window functions. Maybe you’ve had the opportunity to analyze some variables where each value was associated with a time value. Such data – where values are ordered by time – is called time series data.

LearnSQL.com’s New Learning Path: Data Engineering

by LearnSQL.com Team 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.

Using GROUP BY in SQL

by Zahin Rahman 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.

The LAG Function and the LEAD Function in SQL

by Dorota Wdzięczna LAG() and LEAD() are positional functions. A positional function is a type of window function. If you are not familiar with when and how to use them, what the syntax of each function is, why you might want to use them, and what the differences are, read on! LAG() and LEAD() are positional functions. These are window functions and are very useful in creating reports, because they can refer to data from rows above or below the current row.

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

by Tihomir Babic 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.

How to Learn SQL Fast

by Jakub Romanowski Are you in a hurry to improve your data skills? I’ve got good news: you can learn SQL fast and move to a whole new level of data proficiency. You work with data every day, but you've had enough of how long it takes to process your giant table in Excel. The time has come for a much better tool: SQL! But how long does it take to learn SQL?

How to Calculate the Difference Between Two Rows in SQL

by Ignacio L. Bisso Calculating the difference between two rows in SQL can be a challenging task. It is possible – and there’s more than one way to do it. In this article, I’ll explain how to use the SQL window functions LEAD() and LAG() to find the difference between two rows in the same table. I like to think of this as a “happy hour" article – you can learn about two topics (calculating the difference between two rows and SQL window functions) by reading just one article.

What Is Data Engineering?

by Adrian Więch 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.

What Is a CTE?

by Marija Ilic 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.

Top 10 Laptops for Learning SQL in 2020

by Jakub Romanowski 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?

by Agnieszka Kozubek-Krycuń 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.

Why Learn SQL for iOS and Android Development?

by Rebecca McKeown App and program development with iOS and Android is a huge and rapidly growing field in the software world. While some developers get through their careers knowing only their chosen development language, there are plenty of reasons to add SQL to that skill set. Here at LearnSQL.com, we are often asked: “why Learn SQL for iOS and Android development?” To answer that question, we’ve put together a little explanation about exactly why learning SQL makes sense for those in the app development space.

SQL Course of the Month – PostGIS

by Jakub Romanowski 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.

Listen to These 7 SQL Podcasts in 2020

by Marcin Koryszewski Are you learning SQL online but craving more? If you're looking for a way to squeeze some sweet SQL knowledge into your day, try listening to a SQL podcast. Choose one of our picks and get ready to amp up your SQL game! If you're like me, you like to get deep into a topic. You’re practicing it whenever there’s an opportunity. Of course, It’s hard to make time. I cherish the days I’m able to sit down and just get some hands-on learning done.

How ORDER BY and NULL Work Together in SQL

by Kateryna Koidan Do NULL values come first or last when you use ORDER BY? Are they considered higher or lower than non-NULL values? In this article, I’ll explain how different relational databases treat NULL values when sorting output and how to change the default behavior of the ORDER BY clause. When LearnSQL users practice the ORDER BY clause in our SQL Basics course, they often ask why NULL values appear first in the output and how they can change this behavior.

How to Publish a LearnSQL.com Course Certificate on LinkedIn

by Jakub Romanowski 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.

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

by Dorota Wdzięczna 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.

How to Learn the SQL Syntax

by Kate Stolarek Read about what SQL is, and choose the best way for you among a wide variety of possibilities for learning SQL and remembering its syntax. What Is SQL? “SQL” stands for “Structured Query Language,” and as it sounds, it is a language dedicated to querying a relational database. In practice, it is used for creating, designing, and managing a relational database. People use SQL to: Create sets of tables and rows Modify database tables and index structures Insert, update, and delete data Retrieve information from a database for a variety of uses such as analytics Relational databases consist of a set of tables containing rows and columns of data.

A Mathematician in the World of SQL

by Jakub Romanowski 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.

Last-Minute Preparation Tips for a Database Class Exam

by Adrian Więch 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.

How to Practice SQL Window Functions at Home

by Tihomir Babic Are you looking for a way to maintain your knowledge of SQL window functions? What’s the best way to practice them at home? Here are some suggestions. Learning something new feels great, but it’s also arguably the easiest part of gaining knowledge. You’ve probably experienced that yourself. You struggle with learning an idea, and then you finally get it! There’s the feeling you’ve learned something. And then, very soon, you practically have to start all over again with the very same concepts.

The Best SQL Social Media Groups and Channels to Follow in 2020

by Jakub Romanowski We get news, advice, and funny videos from Facebook, Twitter, and YouTube. Why not use social media to help you learn SQL? You wake up and the first thing you do is check for Facebook notifications. Do you take a photo of your breakfast and share it with friends on Instagram? Maybe you argue with someone on Twitter about which James Bond was the best? Or maybe you are recording a short TikTok video of you singing Lady Gaga?

What’s an SQL Inline Query?

by Kamil Bladoszewski Have you ever heard the term “inline query”? How are they different from subqueries and derived tables? Have you looked this up in numerous places and still don’t know the answer? Let’s embark on a journey and find out together! The first time I heard the term “inline query”, I was a little bit surprised. It doesn’t sound like one of SQL’s nuances and I thought I knew all the basic concepts.

Monthly SQL Challenges

by Dorota Wdzięczna SQL learners sometimes need challenges. Do you want to test your problem-solving skills or your knowledge of SQL? Then take our monthly SQL Challenges! We prepare them on LearnSQL.com every month. Each Challenge relates to a different interesting topic and will help you keep your SQL game sharp. In this article, you'll discover what our LearnSQL.com Monthly Challenges are and where to find them. We’ll also look at the Challenges collected in our Monthly SQL Challenge Mini Track.

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

by Kateryna Koidan 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?

SQL Course of the Month – SQL Practice Set

by LearnSQL.com Team 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.

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

by Pierre Timms 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?

Top 5 Programming Languages to Learn Alongside SQL

by Rebecca McKeown 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?

How to Learn SQL JOINs

by Zahin Rahman 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.

What Are the Different Types of SQL Subqueries?

by Kateryna Koidan Subqueries can be used in many business cases. What subquery types does SQL offer? And how can you use them efficiently? In this article, I’ll guide you through different subquery types and the typical situations when they are useful. What Is an SQL Subquery? A subquery, or nested query, is a query placed within another SQL query. There are many different scenarios where you may want to include a query in the WHERE, FROM, or SELECT clauses of your main query.

Subquery vs. JOIN

by Dorota Wdzięczna 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.

5 Advanced SQL Constructions Every Data Analyst Should Learn

by Tihomir Babic Does your job involve data analysis? Here are five examples of how advanced SQL can help you in your daily work. I’m a data analyst and I have to say – data analysts can be quite strange. Other people are usually afraid of immense amounts of data; we enjoy it. The deeper we get into data, the happier we are. An important tool for getting into data (and thus being a happier data analyst) is SQL.

Is it Difficult to Learn SQL?

by Rebecca McKeown It’s the number one question asked by the students of SQL and those new to the IT world. Is it difficult to learn SQL? If you came here because you’ve been pondering that very same question, take some comfort in the fact that in no way are you alone. Even the idea of SQL can be intimidating to those of us without a tech background, but it doesn’t have to be that way.

Subquery vs. CTE: A SQL Primer

by Kamil Bladoszewski Have you ever wondered about the differences between a subquery and a common table expression (CTE) in SQL? The concepts seem very similar, but knowing the difference – and when to use each one – will help you write efficient and readable queries. First, we’ll explain the concepts underlying subqueries and CTEs. Then we’ll look at a few examples and finally analyze the pros and cons of each technique.

How to Number Rows in an SQL Result Set

by Ignacio L. Bisso Have you ever needed to add a sequential number to the records in the result of an SQL query? It’s not as simple as it looks! Find out how to do it correctly in this article. To number rows in a result set, you have to use an SQL window function called ROW_NUMBER(). This function assigns a sequential integer number to each result row. However, it can also be used to number records in different ways, such as by subsets.

SQL Course of the Month – Creating Basic SQL Reports

by LearnSQL.com Team 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?

Overview of Ranking Functions in SQL

by Dorota Wdzięczna SQL ranking functions make working with relational databases easier, especially for data analysts, marketers, and financial specialists. These functions are used to assign a ranking number for each record and allow you to efficiently create useful reports. SQL ranking functions are window functions. Window functions compute the result based on a set of rows. The word “window” refers to this set of rows. Let’s look at the syntax of ranking functions:

Beginner’s Guide to the SQL Subquery

by Ignacio L. Bisso Subqueries are a powerful SQL resource, allowing us to combine data from multiple tables in a single query. In this article, we’ll teach you everything you need to begin using subqueries. Perhaps the simplest definition of a SQL subquery is “A query inside a query”. Subqueries are so easy to understand that they often appear in the opening chapters of SQL courses. However, there are many variants of subqueries that need to be explained.

Advanced SQL Interview Questions (and Answers)

by Tihomir Babic 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.

SQL in Google Sheets? Yes, We Can!

by Adrian Więch Did you know that you can write SQL-like queries in Google spreadsheets? This feature is incredibly powerful, versatile, and can replace most of the functionalities offered by Excel’s pivot tables. Read our article to find out how you can easily use the QUERY function to efficiently work with your Google Sheets data. Relational databases share many features with spreadsheets. When we explain what databases are, we often say that they are a bit like spreadsheets except they give us more control over larger amounts of data.

Why Should I Learn SQL Window Functions?

by Marija Ilic SQL has been around for more than 25 years. Its basic syntax – like SELECT, WHERE, GROUP BY, HAVING, and ORDER BY – is well known. But is there something besides traditional SQL? Can you go beyond the basics and improve your skills? The answer to this question is yes. There is a modern version of SQL. In this article, we are going to dive into the modern version and learn about SQL window functions.

What Is a Nested Query in SQL?

by Kateryna Koidan Have you ever wished that you could build a query with several SELECT statements? Good news! You can do this – and a lot more – with SQL’s nested queries. If you’ve been learning SQL (and maybe writing some queries) for a while, you’ve probably encountered cases where it looks like you need another SELECT statement inside your main statement. You may wonder “Is it possible to use nested SELECTs in SQL?

Advanced SQL Courses for Data Analysts – A Complete Review

by Dorota Wdzięczna 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.

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

by Dorota Wdzięczna 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?

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

by Rebecca McKeown 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 a Programming Language?

by Kateryna Koidan SQL is a powerful tool for communicating with database management systems. When you write SQL queries, you give instructions to the computer, and it performs these instructions—it sounds like programming. However, you cannot build an application with SQL as you can with Python or Java. So, is SQL a programming language? What Is SQL? Let’s start with the basic definition. SQL, or Structured Query Language, is a language used for communication with relational databases.

SQL Course of the Month – Window Functions

by LearnSQL.com Team 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.

What Is a SQL Running Total and How Do You Compute It?

by Dorota Wdzięczna The SQL running total is a very common pattern, used frequently in finance and in trend analysis. In this article, you’ll learn what a running total is and how to write a SQL query to compute it. So, without further ado, let’s get started on the first part of the question. What’s a SQL Running Total? In SQL, a running total is the cumulative sum of the previous numbers in a column.

Is SQL Worth Learning?

by Kate Stolarek 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

by Arleta Więch 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.

When Do I Use SQL Window Functions?

by Tihomir Babic Have you heard one of your colleagues bragging about using SQL window functions? Do you know basic SQL but not much, or anything, about window functions? If you want to learn about window functions and how to use them in a business context, you’re in the right place! This happens often. You reach a certain level of knowledge, and you feel like the king (or queen) of the world.

How to Join 3 Tables (or More) in SQL

by Kamil Bladoszewski 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.

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

by Agnieszka Kozubek-Krycuń 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.

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

by Emil Drkušić 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.

What is the Best SQL Training Online?

by Zahin Rahman In today’s data-driven world, SQL is a highly sought-after skill, but it cannot be mastered merely over a fortnight. With so many resources at your disposal to learn SQL, where do you even consider beginning, and how do you practice SQL? Savvy and knowledgeable database professionals have consistently been in high demand over the last five years. If you are aiming to advance your career as a database developer, administrator, warehousing specialist, or analyst, SQL training and mastery is an absolute necessity.

How to Analyze Time Series COVID-19 Data with SQL Window Functions

by Marija Ilic The COVID-19 pandemic really changed the way we live. No matter where you are, you're being impacted by this unpredictable virus. We do not know what the future holds, but we do believe in science and in better days to come. One thing that makes me as a data analyst particularly happy is that we have publicly available data. We can analyze that data and learn something from it. If you want to explore COVID-19 with the help of modern SQL constructions, keep reading — this article is intended for you.

SQL Window Functions vs. GROUP BY: What’s the Difference?

by Ignacio L. Bisso A very common misconception among SQL users is that there is not much difference between SQL window functions and aggregate functions or the GROUP BY clause. However, the differences are very significant. Perhaps the only similar point between GROUP BY and window functions is that both allow you to execute a function (such as AVG, MAX, MIN, or COUNT) on a group of records. I’d say that window functions’ special power is that they allow us to obtain results that otherwise would be almost impossible to achieve.

Choose the Best Way to Learn SQL

by Arleta Więch 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.

SQL Cookbook with Recipes for Success

by Dorota Wdzięczna 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.

Are There Any Good SQL Courses for Marketers?

by Kate Stolarek 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.

How to Get the First Day of the Week in SQL Server

by Agnieszka Kozubek-Krycuń This is additional content for the LearnSQL.com course Customer Behavior Analysis in SQL Server. In the previous article, we talked about how you can use the SQL Server DATEPART() function with week or iso_week to group events by week. The query might look like this: SELECT DATEPART(week, RegistrationDate) AS Week, COUNT(CustomerID) AS Registrations FROM Customers WHERE '20180101' The result looks something like this: WeekRegistrations 1 58 2 123 .

How to Group Data by Week in SQL Server

by Agnieszka Kozubek-Krycuń This is additional content for the LearnSQL.com course Customer Behavior Analysis in SQL Server. In this course, we showed you how you can analyze the customer lifecycle (customer acquisition, conversion, activity, retention, and churn) with SQL. We discussed customer registration cohorts, or groups of customers who registered during the same period (e.g. same week, same month). Analyzing customer registration cohorts lets you see registration trends and relate registration cohorts with marketing campaigns.

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

by Jakub Romanowski 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.

50 Best Resources for Learning SQL in 2020

by Rebecca McKeown 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.

Why Window Functions Are Not Allowed in WHERE Clauses

by Agnieszka Kozubek-Krycuń Window functions are extremely powerful, but there are a lot of nuances and little details you need to learn about using window functions in order to use them correctly and efficiently. A fairly common question SQL users have is why window functions are not allowed in WHERE. TL;DR: You can use window functions in SELECT and ORDER BY. You cannot use window functions in WHERE, GROUP BY, or HAVING.

How to Practice SQL After a Video Course

by Magdalena Wojtas When you're just starting to learn coding, the most obvious first step is to watch online video courses. They're one of the most popular ways to learn the basics of a new technology without investing a lot of time and money. But you need to do more than that to master the topic. What should be your next step? When someone asks me about how to start learning to code, I often recommend trying video tutorials first.

How to Rank Rows in SQL: A Complete Guide

by Kamil Bladoszewski Don’t struggle with SQL ranking functions anymore! This article will guide you through the most common ranking use cases. Rankings are used around us every day. Sports tournaments, the best movies and TV series on Netflix, stores with the cheapest products—these are only a few examples of rankings you might’ve seen recently. Using SQL RANK functions might be hard sometimes. The variety of different constructions is enormous. You can easily get lost in everything there is to learn about ranking.

How to Practice SQL JOINs

by Emil Drkušić 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?

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

by LearnSQL.com Team 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.

Video Tutorial or Interactive SQL Course – Which Is Better?

by Kate Stolarek Are you ready to get started with SQL but unsure which learning method is the most effective? In this post, we’ll talk about the pros and cons of learning SQL from an instructional video vs. an interactive online course. Are you a chronic Internet-using student who’s planning to learn SQL? Maybe you did some research but still don’t know which kind of training is worth your (limited) time. We all have families, hobbies, and other after-work commitments, and finding the right resource for learning SQL will save you some time.

The Top 7 Platforms with the Best SQL Courses for 2020

by Zahin Rahman Are you struggling to narrow down which platforms are the best for learning SQL online? We have all been there. I know how confusing it can be when choosing amongst the hundreds of resources available. Find out below which platforms offer the most enriching and seamless SQL learning experiences online. In this article, I will review the platforms with the best online SQL courses offered this year. Whether you are a student looking for your first job, a professional hoping to transition to a data analysis, or an experienced data practitioner, there are plenty of great opportunities to learn SQL online at various levels of technical ability.

Learning SQL? 12 Ways to Practice SQL Online

by Rebecca McKeown If you’re currently learning SQL, you may have found yourself knee-deep in reading material and may be wondering how on earth you can bridge the gap between book knowledge and real-life SQL application. In this article, we bring you 12 of the most effective ways to practice SQL online, taking you from a bookworm to a database butterfly in no time at all! All theory and no practice will make you a frustrated SQL user!

How to Stay Healthy When Learning SQL

by Jakub Romanowski 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?

How to Become an SQL Developer

by Emil Drkušić 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.

How Long Does It Take to Learn SQL? Top Tips for SQL Proficiency

by Rebecca McKeown Is it hard to learn SQL? How long does SQL mastery take? This article will answer those questions and get you started with the most useful SQL commands. How long does it take to learn SQL? If you’ve ever dabbled in Spanish or French, you know that learning a new language is tough and can take years. Luckily, mastering SQL is a much faster journey than conquering por/para or un, deux, trois.

HAVING vs. WHERE in SQL: What You Should Know

by Ignacio L. Bisso 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.

19 Top SQL Articles for Beginners Published in 2019

by Dorota Wdzięczna In 2019, a lot of new SQL articles were written for beginners. This kind of resource is useful not only for professionals. SQL articles allow you to develop skills, expand your knowledge, and use SQL in practice. They are a very good way to learn SQL. In this post, I gathered 19 top SQL articles of 2019. Let’s also learn SQL from articles! List of Top SQL Articles Published in 2019 We will start with five of the best articles published on the LearnSQL.

How to Practice SQL

by Jakub Romanowski Do you already know what SQL aggregation functions are, what JOINs are, and how “group by” is different than“order by”? Great, congratulations. But don't you think that in order to master SQL and be able to apply it, you need to practice? We advise you on how to practice SQL to prepare for a data analyst job interview or to simply boost your knowledge effectively. Because, as they say, SQL practice makes perfect.

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

by Rebecca McKeown 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

by Jakub Romanowski 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.

Difference between GROUP BY and ORDER BY in Simple Words

by Shanika Wickramasinghe 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.

Join us on Facebook–We Can Learn More Together

by Jakub Romanowski 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.

Grouping Data in SQL Server

by Belma Mesihovic People who work with data know that data grouping can sometimes be a chore. If you struggle and waste hours with Excel, OpenOffice, or some other tool trying to group various sets of data, take a look at this article and learn how to do the work much quicker and easier by using SQL. You often find yourself in a situation where you need to analyze data and present the results in a form other than the one in which the data is stored.

SQL Order of Operations

by Ignacio L. Bisso SQL is not a traditional programming language in which you write a sequence of instructions in a given order of execution. Instead, SQL is a "declarative" language, which means that by writing a SQL query, you declare what data you expect as a result of the query, but you don't indicate how to obtain it. Six Operations to Order: SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY By using examples, we will explain the execution order of the six most common operations or pieces in an SQL query.

The Most Important SQL Queries for Beginners

by Dorota Wdzięczna How do you get data from a table? How do you create or delete a table? How do you display distinct records? How do you select rows which store a specific value in a column? You can easily do all of this by writing basic SQL queries. This guide discusses the 30 most important SQL queries for beginners. Let's take a look. 1. Retrieving Data From All Columns This is a very basic query to display all data from a table.

YouTube Tutorials That Actually Teach You Some SQL

by Jakub Romanowski 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?

24 Rules to the SQL Formatting Standard

by Dorota Wdzięczna Writing queries to a database requires knowledge about SQL syntax, but this is not all you should know. Best practices for writing professional SQL code require good formatting skills. In this article I discuss why this is so important and what are the basic rules you should follow. Why is it Worthwhile to Format SQL Code? Beginner SQL programmers often don't pay much attention to formatting their code. If you think formatting is something that can be safely ignored, look at the code below:

SQL INNER JOIN Explained in Simple Words

by Ignacio L. Bisso In this article, I will cover perhaps the most important element of the SQL language. That's right! I'm talking about the SQL INNER JOIN clause. As you know, in a database the data are stored in several tables. In my last article, I covered how to create SQL queries when the data you need is in only one table. But what if the data you need is in two tables?

Forget About Excel, High Five With SQL

by Adrian Więch 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.

14 Differences Between Standard SQL and Transact-SQL

by Dorota Wdzięczna In my last article, I roughly described how standard SQL differs from T-SQL and who should learn which. Now I'd like to focus on the syntax differences and illustrate these differences with examples. If you think T-SQL is an extension implementing all the features from standard SQL, you aren't right. However, in SQL Server you will find almost all the features of the SQL standard. In this article you will find examples of some of the differences in syntax between standard SQL and Transact-SQL.

Get to Know the Power of SQL Recursive Queries

by Michał Kołodziejski Most commonly, the SQL queries we run on a database are quite simple. Well, that depends on your role, of course. Analysts in data warehouses retrieve completely different sorts of information using (very often) much more complicated queries than software engineers creating CRUD applications. However, sometimes it's simpler or more elegant to run a query that is a little bit more sophisticated without needing further data processing in the code.

What's the Difference Between SQL and T-SQL?

by Dorota Wdzięczna If you are beginning to learn SQL and are confused by the differences between standard SQL and other similar languages like T-SQL, this article will help make things clear. You’ll not only learn about the difference between SQL and T-SQL but also find explanations concerning which topics would be better to start learning first: standard SQL or something more specific like MS SQL Server. What is Standard SQL? SQL (Structured Query Language) is a basic ANSI/ISO standard programming language designed to operate on data stored in relational databases.

Microsoft SQL Server Pros and Cons

by Roman Pijacek Thinking about using Microsoft SQL Server? If so, you’re in the right place. In this article, we’ll go over the pros and cons of Microsoft SQL Server and evaluate the platform from both a company’s and a data specialist’s perspective. What Is Microsoft SQL Server? Before diving into the pros and cons of Microsoft SQL Server, I’ll explain what it is. In technical terms, it is a relational database management system (RDBMS) developed by Microsoft.

How to Install PostgreSQL on Windows 10 in 5 Minutes

by Ignacio L. Bisso 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

by Aldo Zelen 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

by Dorota Wdzięczna 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

by Ignacio L. Bisso 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.

Our Picks for 2020’s 7 Best Online SQL Schools

by Dorota Wdzięczna 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.

Here’s Why You Should Learn SQL

by Kate Stolarek 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.

5 Great Benefits of Learning SQL

by Alex Briggs 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.

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

by Kacper Skawina 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!