SQL Joins Explained - INNER, LEFT, RIGHT, FULL

Tutorials • 08-Aug-2025

by Roxana Haidiner

When working with databases, your data is often stored in more than one table. But how can you bring the data together?

This is what SQL JOINs are for. A JOIN helps you combine rows from two tables based on a related column, usually a column that appears in both.

Types of SQL JOINs

Here are the most common types of JOINs and what they do:

JOIN Type	What it returns
INNER JOIN	Only rows that exist in both tables
LEFT JOIN	All rows from the left table and matching rows from the right table
RIGHT JOIN	All rows from the right table and matching rows from the left table
FULL JOIN	All rows from both tables

What Is a SQL JOIN?

Let’s say you have:

One table with a list of employees
Another table with a list of departments

Each employee works in a department. If we want to know who works where, we need to connect the tables using a JOIN.

The JOIN compares values in both tables and brings the matching rows together.

Example Tables

Table: Employees

employee_id	name	department_id
1	Sarah James	10
2	Mark White	20
3	Olivia Reed	NULL

Table: Departments

department_id	department_name
10	Engineering
20	Sales
30	HR

INNER JOIN

Returns only employees that are assigned to a department.

SELECT name, department_name
FROM Employees
INNER JOIN Departments
ON Employees.department_id = Departments.department_id;

Result:

name	department_name
Sarah James	Engineering
Mark White	Sales

Employees without a department, and departments with no employees, are not shown.

LEFT JOIN

Returns all employees, even if they don’t belong to any department.

SELECT name, department_name
FROM Employees
LEFT JOIN Departments
ON Employees.department_id = Departments.department_id;

Result:

name	department_name
Sarah James	Engineering
Mark White	Sales
Olivia Reed	NULL

You get all employees. If they have no department, the result will show NULL.

RIGHT JOIN

Returns all departments, even if no employee is assigned to them.

SELECT name, department_name
FROM Employees
RIGHT JOIN Departments
ON Employees.department_id = Departments.department_id;

Result:

name	department_name
Sarah James	Engineering
Mark White	Sales
NULL	HR

You get all departments. If no one works there, the result shows NULL for the name.

FULL JOIN

Returns all employees and all departments. If they match, they are shown together. If not, one side will be NULL.

SELECT name, department_name
FROM Employees
FULL JOIN Departments
ON Employees.department_id = Departments.department_id;

Result:

name	department_name
Sarah James	Engineering
Mark White	Sales
Olivia Reed	NULL
NULL	HR

This gives you the full picture.

Summary

Use INNER JOIN when you want only matching data
Use LEFT JOIN when you want all rows from the first table
Use RIGHT JOIN when you want all rows from the second table
Use FULL JOIN when you want everything, matched or not

How to Do This Visually in DbSchema

You can use DbSchema to build JOINs without writing any SQL.

Drag the two tables into the canvas
Connect them by dragging from one column to the other, to create a foreign key

Foreign Key in DbSchema

Open the Query Builder and cascade related tables

Query Builder in DbSchema

Right-click the line to select the JOIN type
Choose the columns you want to display

Query Builder in DbSchema

Run the query and see the results

Query Builder in DbSchema

This is a great way to learn how JOINs work, because DbSchema auto-generates SQL code for you!

Query Builder in DbSchema

Note: The JOIN types shown in the menu depend on the database you are connected to. Some databases (like SQLite) do not support RIGHT JOIN or FULL JOIN. In these cases, DbSchema will only show the join types supported by your database.