1、完全等于 <=>
mysql> select null <=> null; +---------------+ | null <=> null | +---------------+ | 1 | +---------------+ 1 row in set mysql> select null <=> 18; +-------------+ | null <=> 18 | +-------------+ | 0 | +-------------+ 1 row in set mysql>
注:用于严格比较两个null值是否相等,两个操作码均为null时,其所得值为1;而当一个操作码为null时,其所得值为0。mysql 数据库系统中,1代表true,0代表false。
2、不等于 <>
mysql> select 15 <> 18; +----------+ | 15 <> 18 | +----------+ | 1 | +----------+ 1 row in set mysql>
注:<> 同 !=