How to in Sql

LearnSQL.com Team

Practical Ways to Improve the Performance of SQL Queries

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

Ignacio L. Bisso

How to Begin Running SQL Queries

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

Aldo Zelen

SQL Indexing 101

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

Aldo Zelen

How to Use a SQL Wildcard

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

Aldo Zelen

SQL Filtering 101

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

Kate Stolarek

Why Learn SQL Over the Summer

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

Ignacio L. Bisso

Improving Slow Query Performance: When Runtime Matters

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

Ignacio L. Bisso

Converting Subqueries to Joins

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

Aldo Zelen

Essential SQL Terms to Know for Beginners and Pros

Updated on: April 11, 2024 Working with databases can seem daunting to a non-technical person. Right away, you’re bombarded with new terms that make your head spin. Database, database instance, table, SQL and others are some of the basic terms that you need to understand just to have a normal conversation with your technical colleagues. In this article, we’ll explore some basic SQL database terminology you need to know to succeed.

Ignacio L. Bisso

Learn to Write a SQL Correlated Subquery in 5 Minutes

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

Dorota Wdzięczna

New LearnSQL.com Online Practice: SQL Practice Set

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

Aldo Zelen

How to Become a Database Analyst

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

Ignacio L. Bisso

Extracting Data From a String: SPLIT_PART in PostgreSQL

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

Ignacio L. Bisso

How to Remove Junk Characters in SQL

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

Ignacio L. Bisso

How to Solve Capitalization Data Quality Issues

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

Aldo Zelen

18 Useful Important SQL Functions to Learn ASAP

Updated on: October 30th, 2023 Learning a new programming language can seem intimidating. Like any other language, a programming language has a large vocabulary that you need to master. In this article, we’ll look at some of the most useful SQL functions that you need to know. Structured Query Language, commonly known as SQL, is the standard language for managing and querying data in relational databases. Born out of the need to efficiently interact with large datasets, SQL has become an indispensable tool for database administrators, data analysts, and developers alike.

Aldo Zelen

Simplify SQL Code: Recursive Queries in DBMS

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

Kacper Skawina

Analyzing Survey Data: Explore Results Using SQL

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

Dorota Wdzięczna

SQL Hacks To Control Family Budget On Black Friday Weekend

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

Ignacio L. Bisso

SQL Window Functions By Explanation

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

Marek Pankowski

The 5 Highest Paying Jobs That Use SQL

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

Jenny Hung

Four Reasons You Must Learn SQL in Data Science

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

Kamila Ostrowska

5 Reasons Why No One Should Be Afraid to Learn SQL

Updated on: September 17, 2023 Think SQL is just for tech experts? Think again. In this article, we'll bust some common myths and show you that anyone can learn SQL. Let's dive in and make SQL simple. In today’s world, even those in non-technical jobs need some technical skills. And you don’t have to be a hard-core nerd to get these skills. Everywhere you look, from marketing to management, a touch of tech knowledge can set you apart.

Marek Pankowski

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

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

Marian Dziubiak

Improving Query Readability with Common Table Expressions

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

Marek Pankowski

Complete SQL Practice for Interviews

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

Marian Dziubiak

SQL Development? Structured Query Language and Apps

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

LearnSQL.com Team

The Complete Beginner’s Guide to SQL Fundamentals

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

Maria Alcaraz

Performing Calculations on Date- and Time-Related Values

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

Aldo Zelen

Refine Results with SQL Set Operators

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

Adrian Dembek

6 Common SQL Syntax Mistakes All Learners Make

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

Marcos Pierri

8 Tips Absolute Beginners Can Use to Fix SQL Queries

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

Aldo Zelen

How to Learn SQL: 6 Ideas for Newbies

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

Aldo Zelen

SQL Errors: Five Common SQL Mistakes

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

Aldo Zelen

Five Common SQL Syntax Errors

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