DUAL
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
This page is licensed: GPLv2, originally from fill_help_tables.sql
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