事实上,这个运算符使用的不多,当需要比较 NULL 值的时候,还可以通过 IS NULL 和 IS NOT NULL 来实现:
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mysql> SELECT NULL IS NULL, 1 IS NULL, NULL IS NOT NULL, 1 IS NOT NULL; +--------------+-----------+------------------+---------------+ | NULL IS NULL | 1 IS NULL | NULL IS NOT NULL | 1 IS NOT NULL | +--------------+-----------+------------------+---------------+ | 1 | 0 | 0 | 1 | +--------------+-----------+------------------+---------------+ 1 row in set (0.00 sec)