The reason behind it is that we will not receive any meaningful results from the comparisons when we use NULL with the comparison operators like ‘=’, ‘<’ or ‘<>’. Consider the following example which demonstrates this concept −
mysql> Select 10 = NULL, 10< NULL, 10<>NULL; +-----------+----------+----------+ | 10 = NULL | 10< NULL | 10<>NULL | +-----------+----------+----------+ | NULL | NULL | NULL | +-----------+----------+----------+ 1 row in set (0.07 sec)
The above result set is not meaningful in any sense.