更新时间:2023-11-09 23:04:16
NULL IS NULL将只返回true,因此where子句的那一部分完全没有意义,因为无论topic_id字段发生什么,OR的结果总是为真。
NULL IS NULL will simply return true, hence that part of the where clause is completely pointless, as regardless what happens with the subsidiary_id field, the result of the OR will always be true.