Question

我有一个查询。

DELETE FROM A  
WHERE i NOT IN 
( SELECT i FROM B WHERE j = 1  
  UNION select i from C 
  UNION select i from D 
);

基本上删除A中的所有行，其中字段i未出现在表B，C或D中。如果只是：

DELETE FROM A  
WHERE i NOT IN 
( SELECT i FROM B 
);

然后可以使用左连接轻松完成

DELETE A FROM A 
LEFT JOIN B 
ON A.i = B.i
WHERE B.id is NULL;

（假设每个表在模式中都有一个id字段）

我想我的问题是上面的问题延伸到了具有以下解决方案的三表情景？

DELETE A FROM A 
LEFT JOIN B 
ON A.i = B.i AND B.j = 1
LEFT JOIN C
ON A.i = C.i 
LEFT JOIN D
ON A.i = D.i
WHERE B.id is NULL
AND   C.id is NULL
AND   D.id is NULL

Answer 1

这样的事情：

DELETE 
  FROM A
 WHERE NOT EXISTS (
                   SELECT * 
                     FROM B
                    WHERE B.i = A.i
                  )
       AND NOT EXISTS (
                       SELECT * 
                         FROM C
                        WHERE C.i = A.i
                      )
       AND NOT EXISTS (
                       SELECT * 
                         FROM D
                        WHERE D.i = A.i
                      );

改进mysql查询

1 个答案: