Common Table Expressions (CTEs) are a useful feature in SQL that help simplify complex queries by breaking them down into smaller, more manageable parts. They allow you to write queries that are easier to read and maintain, making your SQL code cleaner and more efficient. Below is a collection of articles from SQL experts at LearnSQL.com that explain how to use CTEs effectively. These resources include detailed guides, practical examples, and exercises to help you master CTEs, whether you're writing basic queries or tackling more advanced tasks. Perfect for both beginners and experienced users, these articles will help you understand how to use CTEs to improve your SQL queries. 19 Jan 2022 Ignacio L. Bisso What Is a Common Table Expression (CTE) in SQL? Updated on: July 19, 2024 The common table expression (CTE) is a powerful construct in SQL that helps simplify a query. CTEs work as virtual tables (with records and columns), created during the execution of a query, used by the query, and eliminated after query execution. A CTE is defined using a CTE query definition, which specifies the structure and content of the CTE. CTEs often act as a bridge to transform the data in source tables to the format expected by the query. Read more 24 Nov 2021 Tihomir Babic Top 5 SQL CTE Interview Questions Here are five questions (and solutions!) on CTEs you’ll (probably) be asked at an interview. I’m not saying you will get these SQL CTE interview questions at every job interview. But when you do, they are probably along the lines of the five I’m about to show here. Other than theoretical questions about CTEs, there are not that many variations in the CTE scenarios evaluated by interviewers. Go through these five examples, and you get a good foundation for acing your interview! Read more 14 May 2024 Gustavo du Mortier 11 SQL Common Table Expression Exercises In this article, we offer you 11 practice exercises that put your knowledge of common table expressions (CTEs) into practice. Each CTE exercise is accompanied by a solution and a detailed explanation. As the saying goes, “A little progress each day adds up to big results”. And that is undoubtedly true for SQL proficiency. Just as you should regularly go to the gym to keep your muscles toned, you should do common table expressions exercises often to keep your querying skills toned for heavy data analysis work. Read more 4 Aug 2020 LearnSQL.com Team Course of the Month: Recursive Queries Recursive Queries is one of SQL’s more advanced features. You could say they divide SQL users into beginners and experts. But how do you learn recursive queries? And why do you need them, anyway? Agnieszka Kozubek-Krycuń, Chief Content Officer at Vertabelo, is here to help. In this article, she answers your questions about our August SQL Course of the Month: Recursive Queries. Recursive queries … that sounds very serious. Read more Latest Articles 1 Oct 2024 Gustavo du Mortier CTE vs. Temporary Table: What’s the Difference? SQL offers you two options to handle complex queries efficiently: CTEs and temporary tables. Read on to weigh the pros and cons of CTEs vs. temp tables. In SQL (Structured Query Language), a common table expression (CTE) lets you define a subquery and assign a name to it so that it can be used within a main query. A temporary table is a database table that you create explicitly, like any other table – but with the particularity that it disappears when you close the database connection in which it was created. Read more 10 Sep 2024 Gustavo du Mortier The MySQL CTE and How to Use It Common table expressions (CTEs) in MySQL give even more versatility to this popular database management system. Find out how to use CTEs to simplify complex queries and implement recursion. All programming languages have ways of simplifying problems by breaking them down into parts that can be solved individually. Users can unify the partial results to obtain a single final result. Thanks to something called common table expressions (CTEs), MySQL is now exception. Read more 16 Jul 2024 Jill Thornhill PostgreSQL CTE: What It Is and How to Use It CTEs, or Common Table Expressions, are a powerful PostgreSQL tool that’s often ignored. This article looks at various PostgreSQL CTEs – including nested and recursive CTEs – and what you can do with them. If you write complex queries in SQL, you’ll soon find that your code becomes cluttered and hard to read. CTEs – also known as WITH clauses – are primarily a way of simplifying queries. However, they also allow you to use recursion. Read more 13 Jun 2024 Gustavo du Mortier SQL CTEs: A Complete Overview of Common Table Expressions This article provides a detailed guide to everything you need to know about common table expressions (CTEs), from the basic definition to the most complex recursive queries. If the database you use supports CTEs, here’s everything you need to get the most out of it. Common table expressions – also called CTEs, WITH clauses, or recursive queries (although this last name is actually a specific application) – are a relatively new feature of SQL. Read more 18 Dec 2023 Ignacio L. Bisso Can You Use Multiple WITH Statements in SQL? A comprehensive guide to multiple WITH statements in SQL, perfect for beginners and experts alike. The SQL WITH clause allows you to define a CTE (common table expression). A CTE is like a table that is populated during query execution. You can use multiple WITH statements in one SQL query to define multiple CTEs. In this article, we will explain how to define multiple CTEs in a single query. Read more 1 Aug 2023 Ignacio L. Bisso CTE in T-SQL: A Beginner’s Guide with 7 Examples A common table expression (CTE) is a powerful T-SQL feature that simplifies query creation in SQL Server. CTEs work as virtual tables (with records and columns) that are created on the fly during the execution of a query. They are consumed by the query and destroyed after the query executes. In some cases – like when the query expects data in a specific format and the source tables have the data in another format – a CTE can act as a bridge to transform the data in the source tables to the format expected by the query. Read more 23 May 2023 Nicole Darnley How to Write a Recursive CTE in SQL Server Updated on: October 23, 2024 This guide will help you understand how to write and use recursive CTEs in SQL Server. Recursive CTEs are powerful tools for handling hierarchical data, and we'll break down their syntax and applications step by step. SQL Server offers a lot of powerful tools for working with data, including Common Table Expressions (CTEs). A CTE is a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement, often referred to as a CTE query. Read more 20 Apr 2023 Jill Thornhill CTE vs. Subquery in SQL: What’s the Difference? What are Common Table Expressions (CTEs)? Are they the same as subqueries? When would you need to use CTEs? This article looks at the similarities and differences between CTE vs subquery. When I introduce a student to Common Table Expressions, their first reaction is “That’s just a subquery! Why do I need to learn that?”. Let’s answer this question by looking at what you can do with an SQL subquery and what extra advantages there are in using a CTE. Read more 21 Feb 2023 Tihomir Babic 6 Useful Examples of CTEs in SQL Server How can you use CTEs in SQL Server in your everyday professional life as a data pro? We’ll answer this question by giving you six examples. CTE is short for Common Table Expression. This is a relatively new feature in SQL Server that was made available with SQL Server 2005. A CTE is a temporary named result. This result is available only for the query that runs it. It isn’t stored, so it doesn't take up disk space. Read more 19 Jan 2023 Tihomir Babic What Is a CTE in SQL Server? What is a CTE, and how do you write a CTE in SQL Server? Join us on a journey where we’ll see all the typical usage of a CTE in SQL Server. CTEs (or Common Table Expressions) are an SQL feature used for defining a temporary named result. You can think of it as a temporary table whose output is available only when the main query is run. This is practical because the CTEs result isn’t stored anywhere but can always be referenced inside the query like any other table. Read more 13 Dec 2022 Tihomir Babic 5 Practical Examples of SQL’s WITH Clause These five practical use cases will make you want to use the SQL WITH clause daily. The WITH clause can help you write readable SQL queries and break complex calculations into logical steps. It was added to SQL to simplify complicated long queries. In this article, we’ll show you 5 practical examples of the WITH clause and explain how using it makes SQL queries more readable. The WITH clause is also called a Common Table Expression (CTE). Read more 29 Sep 2022 Ignacio L. Bisso How the WITH Clause Works in SQL Do you want to master complex SQL queries? Learn how to use the powerful WITH clause! In SQL, there are simple queries and complex queries. A simple query can take data from a table, apply a filter, and return the data as it is in the source table. A complex query may require complex transformations to the source data or may need to read and join data from multiple tables or views. Read more 24 Mar 2022 Tihomir Babic How to Write Multiple CTEs in SQL In this article, I will show you how to leverage the power of multiple CTEs (Common Table Expressions) by combining two or more in a single SQL query. I’ll explain how this technique can simplify complex queries, improve readability, and enhance efficiency when working with large datasets. Common table expressions, or CTEs, can be a powerful SQL tool. When you write two (or even more) CTEs together, this power multiplies. Read more 10 Feb 2022 Tihomir Babic How to Query a Parent-Child Tree in SQL What are parent-child tree structures in SQL? In this article, we answer that question, talk about query hierarchy, and demonstrate the five most common SQL queries you’ll need for these data structures. Yes, you can use SQL on a parent-child tree structure. I’ll show you how in this article. Along the way, I’ll walk you through five query examples, starting with the easiest and ending with the most complex. Read more 19 Oct 2021 Tihomir Babic What Is a Recursive CTE in SQL? The article that’ll show you practical examples of using recursive CTEs in SQL. If you’ve heard about SQL’s recursive CTEs but never used them, this article is for you. It’s also for you if you never get tired of recursive CTE examples. Before we dig into recursion, I’ll remind you what CTEs are and what their syntax is. Then I’ll do the same for recursive CTEs. After that, I’ll show you how recursive CTEs work in three examples. Read more 22 Sep 2021 Tihomir Babic The 7 Best Articles about the SQL Recursive Query Do you want to learn about recursive queries but don’t know where to start? Here’s our selection of seven articles that should help you with diving into the recursive queries world. I won’t lie to you. Learning and understanding recursive queries can be difficult. But difficult things are usually worth trying. And by learning recursive queries, you’re making sure you know how to work with this very powerful tool. Read more 26 Aug 2021 Tihomir Babic 3 Real-Life Examples for SQL Common Table Expressions We answer three SQL business questions using CTEs. There are business problems that are often solved in a very roundabout way. While they might get you the correct result, there’s usually a more elegant way to write a solution. Enter the CTEs! They are extremely helpful when it comes to getting a more direct and elegant solution. I’ll show you three business situations where CTEs can be very helpful. You’ll get an idea of when CTEs can be useful. Read more 18 Aug 2021 Kateryna Koidan 5 Practical SQL CTE Examples Common table expressions (CTEs) were introduced into SQL to improve the readability and the structure of SQL queries, especially those requiring multiple steps to get the necessary output. In this article, we will go through several examples to show how SQL CTEs can help you with complex calculations and hierarchical data structures. Common Table Expressions in SQL Common table expressions (CTEs), also called WITH clauses, allow creating named subqueries that are further referenced in the main query. Read more 15 Jul 2021 Kateryna Koidan 5 Reasons Why You Should Use CTEs Instead of Subqueries Common Table Expressions, or CTEs, were introduced in SQL:1999 to handle cases where the output of one query is used within another query. But didn’t we already have subqueries for this? In this article, I’ll demonstrate with multiple examples why CTEs are better than subqueries for the structure and readability of your SQL queries. Let’s start by reminding ourselves what CTEs and subqueries are and how they differ. Common Table Expressions vs. Read more 10 Jun 2021 Tihomir Babic How to Draw Pictures with Recursive SQL Queries Did you know that SQL can be used for fun? You can even ‘draw’ in SQL using recursive queries! Find out how in this article. As an SQL user, you already know this language is great for data analysis and data manipulation in general. This is something people get very serious about. But you can also have fun with it by drawing ASCII-art pictures using the SQL code. To do that, you have to know how recursive SQL queries work. Read more 7 May 2021 Zahin Rahman What Is the WITH Clause in SQL? Updated on: June 25, 2024 In this article, you will learn about the SQL WITH clause, also known as common table expression (CTE). We will go over some examples to demonstrate some of their use cases in light of their benefits. Today, I'm here to guide you through the intricacies of the SQL WITH clause, commonly known as Common Table Expression (CTE). If you've faced challenges with lengthy and complex SQL queries, this article will be particularly useful. Read more 5 May 2021 Kateryna Koidan A Guide to SQL Common Table Expressions Common table expressions are a relatively new SQL feature that is sometimes overlooked by experienced practitioners working with relational databases. Don’t be one of them! Learn how to use SQL CTEs and join the many data analysts enjoying the benefits of this great tool. Common table expressions (CTEs), also known as WITH clauses, are used to create named subqueries that can be referenced in the main query. CTEs are not saved for future use and can be referenced only within the query where they are defined. Read more 20 Apr 2021 Tihomir Babic Hierarchical Data and How to Query It in SQL How do you recognize hierarchical data, and how do you query it? Two common SQL questions are about to be answered. Querying hierarchical data is a rather common situation if you’re working with SQL and relational databases. Not that hierarchical data is something mystical and rare; on the contrary, it’s everywhere. So why is hierarchical data so challenging when it comes to relational databases? Mainly, the difficulties occur in translating hierarchical data to relational database principles. Read more 8 Apr 2021 Zahin Rahman SQL CTE Explained In this article, you will learn about SQL Common Table Expressions (CTEs). This powerful SQL tool will help you simplify complex queries. Additionally, I will introduce you to the two main types of CTEs and some of their use cases. CTE Primer The Common Table Expression (CTE) was introduced to standard SQL to simplify long, complex queries (especially joins and subqueries). It is a temporary data set returned by a query that contains data separate from the main query. Read more 9 Mar 2021 Kateryna Koidan Why the SQL WITH Clause Is Awesome If you’re not using WITH clauses yet, it’s definitely time to start! SQL WITH clauses, or common table expressions, help improve the structure of SQL queries by making them more readable. That’s already a lot, but WITH clauses have many more benefits. Let’s see together! The WITH clause was introduced in SQL:1999 to define views that are only valid for the query they belong to. Also known as common table expressions (CTEs), WITH clauses allow us to improve the structure of an SQL statement without polluting the database namespace. Read more 5 Mar 2021 Tihomir Babic How to Get Descendants of a Parent in SQL 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. Read more 21 Jan 2021 Zahin Rahman Where Can I Find Good SQL CTE Exercises? Find the top online resources for SQL Common Table Expression (CTE) exercises! CTEs allow you to structure and organize SQL queries efficiently, which is essential if you want to advance your SQL knowledge. A Common Table Expression, or CTE, is a SQL syntax that creates a temporary data set. This set contains separate data than the main query, which can typically be referenced or reused in a subsequent query. A CTE is considered temporary because the result is not permanently stored anywhere and only exists for the duration of the query. Read more 14 Jan 2021 Kateryna Koidan What’s the Difference Between SQL CTEs and Views? SQL views vs. CTEs: What do they do? How are they different? Which one should you use and when? Get your answers here! In SQL, both CTEs (common table expressions) and views help organize your queries, leading to cleaner and easier-to-follow code. However, there are some important differences between them. This article will walk you through several examples of CTEs and views and explain when to use each one. Read more 25 Nov 2020 Tihomir Babic How to Find All Employees Under Each Manager in SQL Have you ever been tasked with building an organizational chart – i.e. finding the employees under each manager in a company? In SQL, you can do that easier than you think! This article will show you how to get the answer using a recursive query. In the business world, it’s a very common task to list all the subordinate employees for a given manager. Is doing this hard enough to warrant a whole article? Read more 28 Oct 2020 Tihomir Babic What are SQL CTE Best Practices? Are you wondering what the best practices for using common table expressions are? This article will help you learn when to use a CTE and how to write it. If you have heard about SQL CTEs, you have probably noticed they’re often mentioned together with subqueries. Sometimes, people think there’s no difference compared to the subqueries, and there’s often debate about whether a CTE or subquery should be used to get a particular result. Read more 23 Oct 2020 Kateryna Koidan How to Learn SQL Common Table Expressions (CTEs) Common table expressions are very useful for organizing, traversing, and improving the readability of long SQL queries. Moreover, recursive CTEs, which can reference themselves, solve problems that cannot be addressed with other queries. But how do you master common table expressions in SQL? In this article, I discuss the most effective strategies for learning CTEs and suggest how to address the common challenges of learning common table expressions on your own. Read more 17 Sep 2020 Tihomir Babic How to Use 2 CTEs in a Single SQL Query Have you ever wondered how to use multiple CTEs in one SQL query? Read this article and find out about recursive CTEs. After learning common table expressions or CTEs, a natural question is “Can I use several CTEs in one query?” Yes, you can! And you can do it quite easily, especially if you already have some basic knowledge of CTEs. Whether you know a bit about CTEs or you’re entirely new to the CTE world, reading about what a CTE is is always a good start. Read more 28 Aug 2020 Adrian Więch How CTEs Work The SQL language offers a feature named Common Table Expressions, or CTEs. Also known as WITH clauses, CTEs are a fairly new addition to SQL. They help you break longer queries into smaller chunks, making your queries much easier to understand. Read the article to find out how to use CTEs and how they differ from traditional subqueries. Common Table Expressions (CTEs), which are essentially named subqueries, were first mentioned in the SQL standard between 1999 and 2000. Read more 26 Aug 2020 Kateryna Koidan SQL CTEs Explained with Examples Learn how you can leverage the power of Common Table Expressions (CTEs) to improve the organization and readability of your SQL queries. The commonly used abbreviation CTE stands for Common Table Expression. To learn about SQL Common Table Expressions through practice, I recommend the interactive Recursive Queries course at LearnSQL.com. It contains over 100 hands-on exercises on simple and complex recursive CTEs. What does a CTE do? Why might you want to use one in your SQL code? Read more 16 Jul 2020 Tihomir Babic When Should I Use a Common Table Expression (CTE)? Interested in hearing more about common table expressions or CTEs? Would you like to know when CTEs are useful? Read on—we’ll discuss in this article. If you’ve heard of common table expressions, you’ve probably wondered what they do. Even if you have not, it’s good that you’re here! CTEs can be very useful, especially if you have already mastered the basics of SQL, such as selecting, ordering, filtering data, and joining tables. Read more 9 Jul 2020 Marija Ilic What Is a CTE? After mastering statements like SELECT, DELETE, INSERT, and GROUP BY, you might search for ways to improve code maintainability, reproducibility, and readability. At that point, you will probably start learning about modern SQL concepts that were introduced in the early 2000s. One such SQL technique is the CTE? (common table expression) —?a temporary named result set. In this article, you will learn what a CTE is and how to use it to improve the maintenance and the readability of your code. Read more 22 May 2020 Kamil Bladoszewski Subquery vs. CTE: A SQL Primer 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. Read more 20 Feb 2019 Michał Kołodziejski Get to Know the Power of SQL Recursive Queries 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. Read more 21 Dec 2017 Aldo Zelen How to Draw a Christmas Tree in SQL You can use SQL to manipulate all kinds of data, from huge analytical queries to brief single-purpose statements. But you can also use SQL just for fun, without any business requirements stifling your creativity. So, get out your jolly hat and prepare to sing O Christmas Tree as we create some quirky art with plain old SQL. Today, we’re going to generate some holiday-themed ASCII art, just for fun. That’s right. Read more 12 Dec 2017 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. Read more 16 Oct 2017 Aldo Zelen How to Organize SQL Queries with CTEs Common table expressions (CTEs) allow you to structure and organize SQL queries. Knowing how to organize SQL queries is a necessity when you begin to move deeper into SQL, so if you want to become an SQL master, you need to know CTEs. The SQL CTE has been part of standard SQL for some time now. CTEs – which are also called WITH statements – are available in all major RDBMS. Read more 10 Oct 2017 Aldo Zelen Long SQL Query vs. Recursive SQL Query Recursion is one of the central ideas in computer science. We can define it as a method for solving problems where the solution of the problem depends on solving a smaller instance of a problem. If this sounds complicated do not fret, in this article we will learn about recursion in SQL that you can practice and deepen at LearnSQL.com. Recursion is a way of solving hierarchical problems we find in data with common SQL. Read more 31 Jul 2017 Marek Pankowski How Recursive Common Table Expressions Work Recursive Common Table Expressions are immensely useful when you're querying hierarchical data. Let's explore what makes them work. Common Table Expressions (CTEs) are some of the most useful constructions in SQL. Their main purpose is improving query design, which makes queries easier to read. One of the reasons CTEs are so popular is that they let you divide longer queries into shorter subqueries. These are easier to read and edit. Read more 30 Mar 2017 Marek Pankowski How to Organize SQL Queries When They Get Long The first long SQL query you’ll have to deal with is likely to be hard for you to structure and understand. These five tips will teach you the best way to organize SQL queries, i.e. write and format them. As we all know, SQL queries are essential to database management. Without them, it would be extremely difficult to find and work with the information in a database. Query length depends on the type of information we need and the size of the database. Read more 22 Mar 2017 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. Read more 26 Nov 2016 Michał Kołodziejski Do it in SQL: Recursive SQL Tree Traversal In the previous article, I described how to use Common Table Expressions to find the shortest path in a directed graph. That example could be hard to follow, I admit. Let’s do something much more common, something that is implemented on almost every website – a menu. Instead of writing the code, we’ll take advantage of the SQL tree structure writing just one query. We’ll use CTEs for PostgreSQL and the hierarchical query clause for Oracle. Read more
Common Table Expressions (CTEs) are a useful feature in SQL that help simplify complex queries by breaking them down into smaller, more manageable parts. They allow you to write queries that are easier to read and maintain, making your SQL code cleaner and more efficient. Below is a collection of articles from SQL experts at LearnSQL.com that explain how to use CTEs effectively. These resources include detailed guides, practical examples, and exercises to help you master CTEs, whether you're writing basic queries or tackling more advanced tasks. Perfect for both beginners and experienced users, these articles will help you understand how to use CTEs to improve your SQL queries.