SQL subqueries are a powerful feature that allows you to write queries within queries, providing a flexible way to retrieve data. They are essential for solving more complex data problems by allowing you to break down your tasks into smaller, manageable parts. Below is a collection of articles that will help you understand and master SQL subqueries. These resources include in-depth guides, tips, and practical exercises designed for both beginners and advanced users, making it easier to incorporate subqueries into your SQL toolkit for more efficient and effective querying. 12 Dec 2023 Martyna Sławińska SQL Subquery Practice: 15 Exercises with Solutions Subqueries are often challenging for beginners. Practice makes perfect, so join us as we work through these 15 SQL subquery practice exercises! In SQL, a subquery is a query nested within another query. It simplifies building intricate queries to retrieve data that meets specific conditions from various tables. In this article, we present various ways of employing subqueries to create complex queries. We start by introducing SQL subqueries along with common use cases. Read more 29 Apr 2024 LearnSQL.com Team 10 Correlated Subquery Exercises with Solutions Correlated subqueries are a powerful SQL feature essential for advanced data analysis. This article provides 10 practical exercises to help you master correlated subqueries. SQL is a fundamental skill for anyone working with data, whether as a data analyst, a SQL developer, a data engineer, or any other related profession. Mastering SQL involves more than just understanding the basics. It also requires learning advanced SQL features, such as subqueries. Read more Latest Articles 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 29 Dec 2022 Ignacio L. Bisso How to Practice SQL Subqueries Have you ever wondered what separates beginners from advanced SQL users? It includes things like, for example, subqueries. In this article, I explain their importance and why you need to practice SQL subqueries to become an expert. What Is an SQL Subquery? SQL is an easy-to-learn language. However, there are certain complex features and techniques of the language that require practice. One of these features is the subquery, which adds great expressive power to the language and your projects. Read more 18 Nov 2021 Kateryna Koidan 5 SQL Subquery Examples SQL subqueries are basic tools if you want to communicate effectively with relational databases. In this article, I provide five subquery examples demonstrating how to use scalar, multirow, and correlated subqueries in the WHERE, FROM/JOIN, and SELECT clauses. A subquery, or nested query, is a query placed within another SQL query. When requesting information from a database, you may find it necessary to include a subquery into the SELECT, FROM , JOIN, or WHERE clause. 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 30 Jul 2020 Ignacio L. Bisso Using Subqueries in INSERT, UPDATE, DELETE Statements 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! Read more 11 Jun 2020 Kamil Bladoszewski What’s an SQL Inline Query? 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. Read more 29 May 2020 Kateryna Koidan What Are the Different Types of SQL Subqueries? 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. Read more 28 May 2020 Dorota Wdzięczna Subquery vs. JOIN One of the challenges in writing SQL queries is choosing whether to use a subquery or a JOIN. There are many situations in which a JOIN is the better solution, and there are others where a subquery is better. Let’s consider this topic in detail. Subqueries are used in complex SQL queries. Usually, there is a main outer query and one or more subqueries nested within the outer query. 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 14 May 2020 Ignacio L. Bisso Beginner’s Guide to the SQL Subquery 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. Read more 7 May 2020 Kateryna Koidan What Is a Nested Query in SQL? Updated on: July 31, 2024 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. Nested queries are an essential part of writing efficient SQL code. If you’ve been learning SQL and writing queries, you’ve likely faced situations where you need to put a SELECT statement inside another SELECT statement. You might wonder, " Read more 15 Feb 2020 How to Find Rows with Minimum Value Problem: You want to find rows which store the smallest numeric value in a column. Example: Our database has a table named weather with data in the following columns: id, city, and temperature. You want to find cities with the lowest temperature. idcitytemperature 1Houston23 2Atlanta20 3Boston15 4Cleveland15 5Dallas34 6Austin28 Solution: SELECT id, city, temperature FROM weather WHERE temperature = (SELECT MIN(temperature) FROM weather); Here’s the result: Read more 15 Feb 2020 How to Find Rows with Maximum Value Problem: You want to find rows which store the largest numeric value in a given column. Example: Our database has a table named student with data in the following columns: id, first_name, last_name, and grade. You want to find the students who have the highest grades. idfirst_namelast_namegrade 1LisaJackson3 2GaryLarry5 3TomMichelin2 4MartinBarker2 5EllieBlack5 6MarySimpson4 Solution: SELECT id, first_name, last_name, grade FROM student WHERE grade = (SELECT MAX(grade) FROM student); Here’s the result: Read more 8 May 2018 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. Read more 10 Apr 2018 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. Read more 13 Dec 2016 Maria Alcaraz Correlated Subquery in SQL: A Beginner’s Guide Sometimes, using a SQL correlated subquery is the only way to solve a statement. But these subqueries can be very slow. In this post, we’ll talk about when to use a correlated subquery, why, and how to do it. Subqueries are an important resource for increasing the expressive power of SQL. If you haven’t read our previous article, subqueries are simply a SELECT statement inside another SELECT. We can use them in different places inside a SELECT, such as in the WHERE, HAVING, or FROM clauses. Read more 18 Nov 2016 Patrycja Dybka SQL Subqueries The article describes what a subquery is and what these useful statements look like. We will cover basic examples with the IN, EXISTS, ANY, and ALL operators, look at subqueries in FROM and WHERE clauses, and explore the difference between correlated and nested subqueries. First, let’s start with an example database. To present some of these statements we need to have an example table and fill it with some data. Read more
SQL subqueries are a powerful feature that allows you to write queries within queries, providing a flexible way to retrieve data. They are essential for solving more complex data problems by allowing you to break down your tasks into smaller, manageable parts. Below is a collection of articles that will help you understand and master SQL subqueries. These resources include in-depth guides, tips, and practical exercises designed for both beginners and advanced users, making it easier to incorporate subqueries into your SQL toolkit for more efficient and effective querying.