DUAL

Understand the DUAL table. This dummy table allows selecting values without referencing a real table, often used for calculations or retrieving system variables.

Description

You can use DUAL instead of a 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 haveFROM 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

• SELECT

_{This page is licensed: GPLv2, originally from fill_help_tables.sql}