DUAL

Description

You are allowed to specify DUAL as a dummy table name in situations where no tables are referenced, such as the following SELECT statement:

SELECT 1 + 1 FROM DUAL;
+-------+
| 1 + 1 |
+-------+
|     2 |
+-------+

DUAL is purely for the convenience of people who require that all SELECT statements should have FROM and possibly other clauses. MariaDB ignores the clauses. MariaDB does not require FROM DUAL if no tables are referenced.

FROM DUAL could be used when you only SELECT computed values, but require a WHERE clause, perhaps to test that a script correctly handles empty resultsets:

SELECT 1 FROM DUAL WHERE FALSE;
Empty set (0.00 sec)

See Also

Comments

Comments loading...
Content reproduced on this site is the property of its respective owners, and this content is not reviewed in advance by MariaDB. The views, information and opinions expressed by this content do not necessarily represent those of MariaDB or any other party.