This tutorial explains how to use the MySQL UNION operator with syntax and examples.
The MySQL UNION operator is used to combine the result sets of 2 or more SELECT statements. It removes duplicate rows between the various SELECT statements.
Each SELECT statement within the UNION operator must have the same number of fields in the result sets with similar data types.
The syntax for the UNION operator in MySQL is:
Parameters or Arguments
expression1, expression2, ... expression_n
The columns or calculations that you wish to retrieve.
The tables that you wish to retrieve records from. There must be at least one table listed in the FROM clause.
Optional. The conditions that must be met for the records to be selected.
Optional. Removes duplicates from the result set, but the inclusion of the DISTINCT modifier has no impact on the result set of the UNION operator because, by default, the UNION operator already removes duplicates.
There must be same number of expressions in both SELECT statements.
Since the UNION operator by default removes all duplicate rows from the result set, providing the UNION DISTINCT modifier has no effect on the results.
The column names from the first SELECT statement in the UNION operator are used as the column names for the result set.
Example - Return single field
The following is an example of the MySQL UNION operator that returns one field from multiple SELECT statements (and both fields have the same data type):
In this MySQL UNION operator example, if a supplier_id appeared in both the suppliers and order_details table, it would appear once in your result set. The MySQL UNION operator removes duplicates. If you do not wish to remove duplicates, try using the MySQL UNION ALL operator.
Example - Using ORDER BY
The MySQL UNION operator can use the ORDER BY clause to order the results of the query.
In this MySQL UNION operator, since the column names are different between the two SELECT statements, it is more advantageous to reference the columns in the ORDER BY clause by their position in the result set. In this example, we've sorted the results by supplier_name / company_name in ascending order, as denoted by the ORDER BY 2.
The supplier_name / company_name fields are in position #2 in the result set.