How To Use UNION Operator In SQL

In this article, we will learn how to use the UNION operator in SQL.

To combine the result-set of multiple SELECT statements, the UNION operator is used.

• Within UNION each SELECT statement must have the same number of columns.
• The columns must also have similar data types.
• The columns must also be in the same order in each SELECT statement.

Syntax

SELECT column_name(s) FROM TABLE_NAME1
UNION
SELECT column_name(s) FROM TABLE_NAME2;

Example

The subsequent statement would select the names (only distinct values) from both the “Viewers” and the “Authors” table:

SELECT Name FROM Viewers
UNION
SELECT Name FROM Authors
ORDER BY Name;

Note : By default, the UNION operator selects only distinct values. To allow duplicate values, use UNION ALL.

Example

The subsequent statement would select the names (duplicate values also) from both the “Viewers” and the “Authors” table:

SELECT Name FROM Viewers
UNION ALL
SELECT Name FROM Authors
ORDER BY Name;

 

Also, check How To Use CROSS JOIN Keyword In SQL