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
