MySQL JOINS are used with SELECT statement. It is used to retrieve data from multiple tables. It is performed whenever you need to fetch records from two or more tables.

What are JOINS?

Joins help retrieving data from two or more database tables. The tables are mutually related using primary and foreign keys.

Note: JOIN is the most misunderstood topic amongst SQL leaners. For sake of simplicity and ease of understanding , we will be using a new Database to practice sample

MySQL Joining Tables

A JOIN clause is used to combine rows from two or more tables, based on a related column between them.

Let’s look at a selection from the “Orders” table:

Then, look at a selection from the “Customers” table:

Notice that the “CustomerID” column in the “Orders” table refers to the “CustomerID” in the “Customers” table. The relationship between the two tables above is the “CustomerID” column. Then, we can create the following SQL statement (that contains an INNER JOIN), that selects records that have matching values in both tables:

Example

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate<br>FROM Orders<br>INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;

and it will produce something like this:

Supported Types of Joins in MySQL

• INNER JOIN: Returns records that have matching values in both tables
• LEFT JOIN: Returns all records from the left table, and the matched records from the right table
• RIGHT JOIN: Returns all records from the right table, and the matched records from the left table
• CROSS JOIN: Returns all records from both tables

MySQL INNER JOIN Keyword

The INNER JOIN keyword selects records that have matching values in both tables.

INNER JOIN Syntax

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the “Orders” table:

And a selection from the “Customers” table:

MySQL INNER JOIN Example

The following SQL statement selects all orders with customer information:

Example

SELECT Orders.OrderID, Customers.CustomerName<br>FROM Orders<br>INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

Note: The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns. If there are records in the “Orders” table that do not have matches in “Customers”, these orders will not be shown!

JOIN Three Tables

The following SQL statement selects all orders with customer and shipper information:

Example

SELECT ;Orders.OrderID, Customers.CustomerName, Shippers.ShipperName<br>FROM ;((Orders<br>INNER;JOIN;Customers;ON;Orders.CustomerID = Customers.CustomerID)<br>INNER;JOIN;Shippers;ON;Orders.ShipperID = Shippers.ShipperID);

MySQL LEFT JOIN Keyword

The LEFT JOIN keyword returns all records from the left table (table1), and the matching records (if any) from the right table (table2).

LEFT JOIN Syntax

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database. Below is a selection from the “Customers” table:

And a selection from the “Orders” table:

MySQL LEFT JOIN Example

The following SQL statement will select all customers, and any orders they might have:

Example

SELECT Customers.CustomerName, Orders.OrderID<br>FROM Customers<br>LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID<br>ORDER BY Customers.CustomerName;

Note: The LEFT JOIN keyword returns all records from the left table (Customers), even if there are no matches in the right table (Orders).

MySQL RIGHT JOIN Keyword

The RIGHT JOIN keyword returns all records from the right table (table2), and the matching records (if any) from the left table (table1).

RIGHT JOIN Syntax

SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name;

Demo Database

In this tutorial we will use the well-known Northwind sample database. Below is a selection from the “Orders” table:

And a selection from the “Employees” table:

MySQL RIGHT JOIN Example

The following SQL statement will return all employees, and any orders they might have placed:

Example

SELECT ;Orders.OrderID, Employees.LastName, Employees.FirstName<br>FROM;Orders<br>RIGHT&;JOIN;Employees;ON&;Orders.EmployeeID = Employees.EmployeeID<br>ORDER;BY;Orders.OrderID;

SQL CROSS JOIN Keyword

The CROSS JOIN keyword returns all records from both tables (table1 and table2).

CROSS JOIN Syntax

SELECT column_name(s)
FROM table1
CROSS JOIN table2;

Note: CROSS JOIN can potentially return very large result-sets!

Demo Database

In this tutorial we will use the well-known Northwind sample database. Below is a selection from the “Customers” table:

And a selection from the “Orders” table:

MySQL CROSS JOIN Example

The following SQL statement selects all customers, and all orders:

Example

SELECT Customers.CustomerName, Orders.OrderID<br>FROM Customers<br>CROSS JOIN Orders;

Note: The CROSS JOIN keyword returns all matching records from both tables whether the other table matches or not. So, if there are rows in “Customers” that do not have matches in “Orders”, or if there are rows in “Orders” that do not have matches in “Customers”, those rows will be listed as well.

If you add a WHERE clause (if table1 and table2 has a relationship), the CROSS JOIN will produce the same result as the INNER JOIN clause:

Example

SELECT&nbsp;Customers.CustomerName, Orders.OrderID<br>FROM&nbsp;Customers<br>CROSS&nbsp;JOIN&nbsp;Orders<br>WHERE&nbsp;Customers.CustomerID=Orders.CustomerID;

MySQL Self Join

A self join is a regular join, but the table is joined with itself.

Self Join Syntax

SELECT column_name(s)
FROM table1 T1, table1 T2
WHERE condition;

T1 and T2 are different table aliases for the same table.

Demo Database

In this tutorial we will use the well-known Northwind sample database. Below is a selection from the “Customers” table:

MySQL Self Join Example

The following SQL statement matches customers that are from the same city:

Example

SELECT&nbsp;A.CustomerName&nbsp;AS&nbsp;CustomerName1, B.CustomerName&nbsp;AS&nbsp;CustomerName2,&nbsp;A.City<br>FROM&nbsp;Customers A, Customers B<br>WHERE&nbsp;A.CustomerID &lt;&gt; B.CustomerID<br>AND&nbsp;A.City = B.City<br>ORDER&nbsp;BY&nbsp;A.City;