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
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