MySQL Tutorial/Comparison Functions Operators/NULL safe equal

NULL-safe equal :<=>

NULL-safe equal(<=>) performs an equality comparison like the = operator.

NULL-safe equal(<=>) returns 1 rather than NULL if both operands are NULL.

NULL-safe equal(<=>) returns 0 rather than NULL if one operand is NULL.

mysql>
mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
+---------+---------------+------------+
| 1 <=> 1 | NULL <=> NULL | 1 <=> NULL |
+---------+---------------+------------+
|       1 |             1 |          0 |
+---------+---------------+------------+
1 row in set (0.00 sec)
mysql>
mysql> SELECT 1 = 1, NULL = NULL, 1 = NULL;
+-------+-------------+----------+
| 1 = 1 | NULL = NULL | 1 = NULL |
+-------+-------------+----------+
|     1 |        NULL |     NULL |
+-------+-------------+----------+
1 row in set (0.00 sec)
mysql>