<=>NULL-safe equal operator. It performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand is NULL.
a <=> b is equivalent to a = b OR (a IS NULL AND b IS NULL).
When used in row comparisons, these two queries return the same results:
See also .
This page is licensed: GPLv2, originally from
SELECT (t1.a, t1.b) <=> (t2.x, t2.y)
FROM t1 INNER JOIN t2;
SELECT (t1.a <=> t2.x) AND (t1.b <=> t2.y)
FROM t1 INNER JOIN t2;SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
+---------+---------------+------------+
| 1 <=> 1 | NULL <=> NULL | 1 <=> NULL |
+---------+---------------+------------+
| 1 | 1 | 0 |
+---------+---------------+------------+
SELECT 1 = 1, NULL = NULL, 1 = NULL;
+-------+-------------+----------+
| 1 = 1 | NULL = NULL | 1 = NULL |
+-------+-------------+----------+
| 1 | NULL | NULL |
+-------+-------------+----------+