Summary: in this tutorial, you will learn how to use the MySQL RIGHT JOIN
to query data from two tables.
Introduction to MySQL RIGHT JOIN clause
MySQL RIGHT JOIN
is similar to LEFT JOIN,
except that the treatment of the joined tables is reversed.
Here’s the syntax of the RIGHT JOIN
of two tables t1
and t2
:
SELECT
select_list
FROM t1
RIGHT JOIN t2 ON
join_condition;
Code language: SQL (Structured Query Language) (sql)
In this syntax:
- The
t1
is the left table andt2
is the right table. - The
join_condition
specifies the rule for matching rows from both tables.
If the join_condition
uses the equal operator (=
) and the joined columns of both tables have the same name, and you can use the USING
syntax like this:
SELECT
select_list
FROM t1
RIGHT JOIN t2 USING(column_name);
Code language: SQL (Structured Query Language) (sql)
Therefore, the following join conditions are equivalent:
ON t1.column_name = t2.column_name
Code language: SQL (Structured Query Language) (sql)
and
USING (column_name);
Code language: SQL (Structured Query Language) (sql)
How the RIGHT JOIN
works.
The RIGHT JOIN
starts selecting data from the right table (t2
). It matches each row from the right table with every row from the left table. If both rows cause the join condition to evaluate to TRUE
, the RIGHT JOIN
combines columns of these rows into a new row and includes this new row in the result set.
If a row from the right table does not have a matching row from the left table, the RIGHT JOIN
combines columns of rows from the right table with NULL
values for all columns of the right table into a new row and include this row in the result set.
In other words, the RIGHT JOIN
returns all rows from the right table regardless of having matching rows from the left table or not.
It’s important to emphasize that RIGHT JOIN
and LEFT JOIN
clauses are functionally equivalent, and they can replace each other as long as the table order is reversed.
Notice that the RIGHT OUTER JOIN
is a synonym for RIGHT JOIN
. Therefore, you can use them interchangeably.
MySQL RIGHT JOIN clause examples
We’ll use the tables employees
and customers
from the sample database for the demonstration:
The column salesRepEmployeeNumber
in the table customers
links to the column employeeNumber
in the employees
table.
A sales representative, or an employee, may be in charge of zero or more customers. And each customer is taken care of by zero or one sales representative.
If the value in the column salesRepEmployeeNumber
is NULL, which means the customer does not have any sales representative.
1) Simple MySQL RIGHT JOIN example
This statement uses the RIGHT JOIN
clause join the table customers
with the table employees
.
SELECT
employeeNumber,
customerNumber
FROM
customers
RIGHT JOIN employees
ON salesRepEmployeeNumber = employeeNumber
ORDER BY
employeeNumber;
Code language: SQL (Structured Query Language) (sql)
In this example:
- The
RIGHT JOIN
returns all rows from the tableemployees
whether rows in the tableemployees
have matching values in the columnsalesRepEmployeeNumber
of the tablecustomers
. - If a row from the table
employees
has no matching row from the tablecustomers
, theRIGHT JOIN
usesNULL
for thecustomerNumber
column.
2) Using MySQL RIGHT JOIN to find unmatching rows
The following statement uses the RIGHT JOIN
clause to find employees who are not in charge of any customers:
SELECT
employeeNumber,
customerNumber
FROM
customers
RIGHT JOIN employees ON
salesRepEmployeeNumber = employeeNumber
WHERE customerNumber is NULL
ORDER BY employeeNumber;
Code language: SQL (Structured Query Language) (sql)
Summary
- MySQL
RIGHT JOIN
allows you to query data from two or more related tables. - The
RIGHT JOIN
starts selecting rows from the right table. It always returns rows from the right table whether or not there are matching rows in the left table. - The
RIGHT OUTER JOIN
is the synonym of theRIGHT JOIN
.