JOIN

LearnSQL.com Team

Course of the Month: SQL JOINs

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

LearnSQL.com Team

SQL JOIN Cheat Sheet

Ready to master SQL JOINs? Get your downloadable cheat sheet now! Your shortcut to becoming an SQL JOINs expert is one click away. Dive deep into the world of SQL JOINs with our detailed SQL JOIN Cheat Sheet, a must-have resource for data enthusiasts at every level. Whether you are just starting out or looking to sharpen your skills, this guide is tailored to provide you with the quick reference needed to use SQL JOINs efficiently.

Tihomir Babic

SQL Joins: 12 Practice Questions with Detailed Answers

In this article, we dig into our SQL JOINS course and give you 12 join exercises to solve. But don’t worry – all the exercises have solutions and explanations. If you get stuck, help is there! This is, after all, made for practicing and learning.  SQL joins can be tricky. It’s not just the syntax, but also knowing what joins to use in what scenarios. Joins are used when combining data from two or more tables in SQL.

Andrew Bone

The Top 10 SQL JOIN Interview Questions with Answers

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.

Patrycja Dybka

SQL JOINs Explained with Venn Diagrams

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

Dorota Wdzięczna

How to Join Two Tables in SQL

Querying data from multiple tables is very common when working with relational databases. It is not difficult if you know how to use the dedicated SQL operators for doing this. In this article, you will learn how to join two tables by using WHERE and by using a special operator JOIN, and you will see how to filter rows in the result set. If you want to practice joining tables in SQL, check out our interactive SQL JOINs course.

Kamil Bladoszewski

How to Join 3 Tables (or More) in SQL

Using JOIN in SQL doesn’t mean you can only join two tables. You can join 3, 4, or even more! The possibilities are limitless. The best way to practice SQL JOINs is LearnSQL.com's interactive SQL JOINs course. It contains over 90 hands-on exercises that let you refresh your SQL JOINs knowledge. It covers a wide range of topics from simple 2-table JOINs, through joining multiple tables and using OUTER JOINs, to joining a table with itself.

Tihomir Babic

What Is a LEFT OUTER JOIN in SQL? 4 Practical Examples

Today’s article will discuss the LEFT OUTER JOIN in SQL. We’ll go through several examples of typical LEFT OUTER JOIN usage and compare it with INNER JOIN. A JOIN is an SQL feature that allows you to combine data from two or more tables. The nature of relational databases makes JOIN one of the most commonly used features in SQL. There are many different types of JOINs. We’ll focus on LEFT OUTER JOIN here.

Kateryna Koidan

How to LEFT JOIN Multiple Tables in SQL

Can you LEFT JOIN three tables in SQL? Yes, indeed! You can use multiple LEFT JOINs in one query if needed for your analysis. In this article, I will go through some examples to demonstrate how to LEFT JOIN multiple tables in SQL and how to avoid some common pitfalls when doing so. The best way to practice different types of joins is our interactive SQL JOINs course. It contains over 90 hands-on exercises that cover simple 2-table joins, joining multiple tables, LEFT JOIN, FULL JOIN, and many more.

Jakub Romanowski

Your Complete Guide to SQL JOINs (with Resources)

This detailed guide covers all important SQL JOIN topics, from basic concepts to advanced techniques. Bookmark this guide for future reference – it’s packed with useful resources and guides to help you work with JOINs effectively. SQL JOINs are essential in SQL and data analysis, as they let you combine data from different tables into a unified view. In this article, I've gathered everything you need to know about SQL JOINs.

Gustavo du Mortier

INNER JOIN vs. OUTER JOIN: What’s the Difference?

Deciding when to use INNER JOIN vs. OUTER JOIN is often challenging for beginners. In this article, you will find explanations and examples that will help you better understand the difference between these two joins. In SQL, JOINs allow you to combine data from different tables; INNER JOIN and OUTER JOIN are simply types of JOIN statements. Understanding their differences is critical if you work with relational databases. It is also crucial if you’re going for an SQL job interview: the difference between INNER JOIN and OUTER JOIN is among the most frequently asked SQL interview questions.

Maria Durkin

What Is CROSS JOIN in SQL?

What is a CROSS JOIN in SQL, and when should you use it? We answer those questions – and give you some examples of CROSS JOIN you can practice for yourself – in this article. CROSS JOINs, a type of SQL JOIN, create all possible row combinations from two tables. If you're new to JOINs and want to learn more, check out our comprehensive SQL JOINs course, which includes over 90 hands-on exercises on various JOIN types.

Radu Gheorghiu

RIGHT JOIN in SQL: A Beginner's Tutorial

Learn RIGHT JOIN, a crucial command for any SQL specialist. Our article breaks down this essential technique, helping beginners effortlessly navigate and apply RIGHT JOIN in their database queries. In SQL, RIGHT JOIN (also known as RIGHT OUTER JOIN) is crucial for handling data effectively. This article is a beginner-friendly guide to the SQL RIGHT JOIN, an essential technique for merging different data tables. We'll walk you through the specifics of RIGHT JOIN, explaining how it stands apart from other join types in managing data.

Tihomir Babic

9 Practical Examples of SQL LEFT JOIN

LEFT JOIN is one of SQL's most common JOINs. Make sure you know all its ins and outs by going through all nine of our real-life LEFT JOIN examples. LEFT JOIN – alongside INNER JOIN – is one of the essential SQL tools you need to work with data from two or more tables. But how and when should you use it? These nine LEFT JOIN examples will point the way.

Martyna Sławińska

5 Easy SQL INNER JOIN Examples for Beginners

Looking for a clear explanation of joins in SQL? Check out these five INNER JOIN examples! In SQL, INNER JOINs can be difficult for beginners to master. But once you start working with them, you’ll learn they’re very useful! Let’s discuss five examples of SQL INNER JOINs. But first, let’s do a quick review of why JOINs matter. In relational databases, data is organized and stored within tables. Each table represents a specific type of information.

Tihomir Babic

What Is FULL JOIN in SQL? An Explanation with 4 Examples

What is FULL JOIN – one of the often neglected SQL join types? In this article, we’ll show you how useful FULL JOIN  can be and teach you how to apply it to different scenarios. The four examples cover some of the typical uses. An SQL join is a construction for combining data from two or more tables. FULL JOIN is one of the types of joins. You’ll get the most from this article if you’re already familiar with SQL joins and how they work.

Dominika Florczykowska

How to Write Multiple Joins in One SQL Query

Have you ever wondered how multiple joins work? Want to know how to join multiple tables in one query? Read this article to find out! If you are just beginning your SQL journey, you may have found it difficult to understand the concept of SQL JOINs, especially if you have to join more than two tables in one query. Worry not! In this article, we will explore how JOIN works and solve all its mysteries!

Dmitri Vaitkun

What Are the Different SQL JOIN Types?

You just can’t understate the importance of the JOIN when learning SQL. Not only is it one of the most fundamental operations in relational databases, but it is also very versatile with many different types. Although SQL JOIN may be intimidating at first, it becomes a very handy instrument in your arsenal once you understand it. Let’s explore all the SQL JOIN types! We can safely say the JOIN operation is one of the most powerful features of SQL.

Himanshu Kathuria

What Is the OUTER JOIN in SQL?

Even if you are new to SQL, you must have come across the term OUTER JOIN. In this article, I will explain what OUTER JOIN in SQL does. I’ll use some practical examples to demonstrate how it is used in day-to-day SQL applications. If you want to use SQL for practical purposes, learning the different JOINs is extremely important. In fact, you will be using a JOIN in just about every second query you write.

Kateryna Koidan

How to Keep Unmatched Rows From Two Tables in a SQL JOIN

Are you looking to join two tables in SQL without removing unmatched rows? Do you want to keep unmatched rows from one or both tables? In this article, I’ll explain how to keep all the records you want by using outer JOINs, such as LEFT JOIN, RIGHT JOIN, and FULL JOIN. Examples included! The SQL JOIN is a powerful tool that helps you combine data from multiple tables of your database.

Kateryna Koidan

How Do You Get Rid of Duplicates in an SQL JOIN?

Do you have unwanted duplicates from your SQL JOIN query? In this article, I’ll discuss the possible reasons for getting duplicates after joining tables in SQL and show how to fix a query depending on the reason behind the duplicates. Data analysts with little experience in SQL JOINs often encounter unwanted duplicates in the result set. It’s challenging for beginners to identify the reason behind these duplicates in JOINs.

Tihomir Babic

How to Join Tables in SQL Without Using JOINs

Here’s how you can combine tables without the JOIN keyword. It seems like it shouldn’t be possible: join tables in SQL without using the JOIN keyword. But using the JOIN keyword is not the only way to join tables in SQL. This article will show you two additional methods for joining tables. Neither of them requires the JOIN keyword to work. They are: Using a comma between the table names in the FROM clause and specifying the joining condition in a WHERE Using UNION and UNION ALL.

Kateryna Koidan

5 Best Practices for Writing SQL JOINs

These best practices for SQL JOINs will help you make readable SQL queries that deliver accurate, clear, and understandable output. Considering that relational databases are built around related tables, it’s no wonder that SQL JOINs – which allow you to combine information from multiple tables – are one of the primary skills acquired by SQL newbies. SQL JOINs course by LearnSQL.com is the perfect place to refresh your knowledge about JOINs.

How to Get all Row Combinations From Two Tables in SQL

Problem You want to get all combinations of rows from two tables in SQL. Example Here are two tables: one contains letters (letters), and the other contains numbers (numbers): letter X Y number 0 1 2 Solution 1 In order to combine every row of the letters table with every row of the numbers table, we will use the CROSS JOIN:

Kateryna Koidan

How to Join Only the First Row in SQL

In your projects, you may encounter situations when you only need to join the first row with the most recent order to the corresponding record in another table. In this article, I’ll go through several ways to do this in SQL. The best way to practice basic and advanced SQL is our interactive SQL Practice track. It contains 10 SQL practice courses with onver 1000 hands-on exercises to help you refresh your SQL skills.

Kamila Ostrowska

Best Places to Practice SQL JOINs Online

You’ve just started your journey with SQL and you’re not sure what a JOIN is or where to use it. Don’t worry! In this article, you will find out what JOINs are and where you can practice them online. If you have just started learning SQL, you have a lot of topics to cover before you can call yourself a data professional. If you are serious about using SQL, you’ll have to understand JOIN – what it does, when you can use it, and what its different variants do.

Andrew Bone

How to Use Aliases with SQL JOINs

SQL aliases are custom names that you can give to the columns and tables you include in your queries. Aliases are very useful, as they can greatly improve the readability and maintainability of your query. We’ll be taking a closer look at using SQL aliases with JOIN and why you might need to do so. The best way to master aliases in SQL is practice. I recommend our interactive SQL Practice Set course.

Kateryna Koidan

What Is the Difference Between WHERE and ON in SQL JOINs?

When you join tables in SQL, you may have conditions in an ON clause and in a WHERE clause. Many get confused by the difference between them. In this article, we will discuss this topic by first reminding you the purpose of the ON and WHERE clauses then by demonstrating with examples which types of conditions should be in each of these clauses. Both the ON clause and the WHERE clause can specify conditions.

Tihomir Babic

How to Keep Unmatched Rows When You Join two Tables in SQL

Learn how to use JOIN to keep both matched and unmatched rows when you join two tables. Joining two or more tables is a skill you need a lot if you’re working with databases. To review and practice your SQL joining skills, I recommend the interactive SQL JOINs course. It contains over 90 exercises and sections on different joining challenges. If you often join tables in SQL, you’ve probably noticed not all data from one table corresponds to data from another table all the time.

Kateryna Koidan

4 Ways to Learn Which JOIN to Use in a SQL Query

You probably already know that you should use JOIN to combine data from several tables. But what kind of JOIN? In this article, I’ll introduce four simple ways to finally learn which JOIN to use in different scenarios. Before we jump into smart strategies for learning SQL JOINs, I suggest taking a brief overview of the major JOIN types. We’ll go through several examples to recall the difference between (INNER) JOIN, LEFT (OUTER) JOIN, RIGHT (OUTER) JOIN, and FULL (OUTER) JOIN.

Zahin Rahman

What FULL JOIN Is and When to Use It

Learn about FULL JOIN, how to implement it, how it compares with the other types of SQL JOINs, and some of its unique use cases. Before we jump into FULL JOINs, let’s quickly recap what an SQL JOIN is. At its core, a JOIN combines data from two or more tables within a database. Tables are usually linked together using unique identifiers in each table, i.e. primary and foreign keys.

Kateryna Koidan

7 SQL JOIN Examples With Detailed Explanations

Do you need to join several tables to get the necessary result set? The SQL JOIN is a basic yet important tool used by data analysts working with relational databases. And I understand it can be difficult to choose from the zillions of introductory guides to joins. In this article, I will focus on real-world examples with detailed explanations. Introduction to JOIN With relational databases, the information you want is often stored in several tables.

Tihomir Babic

SQL JOIN Topics That Require Practice

Are you interested in learning how to join tables in SQL? Where do you start? Many JOIN topics require practice. In this article, we’ll explore these topics by writing codes to solve real-life situations. Hopefully, you will learn which JOIN topics require attention. To make it easier for you, the topics are divided into beginner, intermediate, and advanced. Joining two or more tables in SQL lifts data analysis to another level.

Kateryna Koidan

How to JOIN Tables in SQL

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.

Kateryna Koidan

What Is LEFT JOIN in SQL?

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

Tihomir Babic

SQL JOIN Tips for Beginners

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

Dorota Wdzięczna

What Is an SQL INNER JOIN?

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

Marija Ilic

SQL JOIN Types Explained

What’s the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN in SQL? When should you use each one? We’ve got your answers right here. You want to combine data from two or more different tables, but you’re not sure how to do it in SQL. There are different SQL JOIN types that you can use for different results. If you want to learn the differences between INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN, keep reading.

Martyna Sławińska

What Is a Self Join in SQL? Explaned With 7 Examples

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

Marija Ilic

How to Join the Same Table Twice

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

Kateryna Koidan

Can you Join two Tables Without a Common Column?

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

Kateryna Koidan

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

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

Kateryna Koidan

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

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

Zahin Rahman

How to Learn SQL JOINs

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

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.

Emil Drkušić

How to Practice SQL JOINs

There is no better way to learn how to practice SQL joins than through hands-on experience. 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! Diving into the world of databases? Then you've likely come across SQL joins.

How to Join on Multiple Columns

Problem You want to join tables on multiple columns by using a primary compound key in one table and a foreign compound key in another. Example Our database has three tables named student, enrollment, and payment. The student table has data in the following columns: id (primary key), first_name, and last_name. idfirst_namelast_name 1EllieWillson 2TomBrown 3SandraMiller The enrollment table has data in the following columns: primary key (student_id and course_code), is_active, and start_date.

Ignacio L. Bisso

SQL INNER JOIN Explained in Simple Words

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?

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.

Dorota Wdzięczna

An Illustrated Guide to Multiple Join

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

Dorota Wdzięczna

An Illustrated Guide to the SQL Non Equi Join

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

Dorota Wdzięczna

An Illustrated Guide to the SQL Self Join

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

Marija Ilic

How to Track Down Duplicate Values in a Table

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

Dorota Wdzięczna

An Illustrated Guide to the SQL OUTER JOIN

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

Dorota Wdzięczna

An Illustrated Guide to the SQL INNER JOIN

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

Dorota Wdzięczna

An Illustrated Guide to the SQL CROSS JOIN

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

Francisco Claria

An Introduction to Using SQL Aggregate Functions with JOINs

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

Francisco Claria

Learning JOINs With Real World SQL Examples

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

Adrian Dembek

SQL JOINs for Beginners

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