仅当一组列的所有值相等时，SQL才会删除行

Question

考虑两个表

表a：

Fields :  
- a_ID1  
- a_Status     
- a_Key  

表b：

Fields :  
- b_ID  
- b_Status  
- FK_a_key  

有没有办法从两个表中删除一组关于以下条件的行：
删除FK_a_key = xxx and a_key = xxx的每一行 但是，只有当这些行的状态字段都不是“2”时才会出现？

Answer 1

几个not exists来电应该可以解决问题：

DELETE FROM a
WHERE  a_key = 'xxx' AND 
       NOT EXISTS (SELECT *
                   FROM   a
                   WHERE  a_key = 'xxx' AND a_status != 2) AND
       NOT EXISTS (SELECT *
                   FROM   b
                   WHERE  FK_a_key = 'xxx' AND b_status != 2)


DELETE FROM b
WHERE  b_key = 'xxx' AND 
       -- Frankly, both these conditions are are redundant - 
       -- they've been checked in the previous statement
       NOT EXISTS (SELECT *
                   FROM   a
                   WHERE  a_key = 'xxx' AND a_status != 2) AND
       NOT EXISTS (SELECT *
                   FROM   b
                   WHERE  FK_a_key = 'xxx' AND b_status != 2)