Question

我惹恼了一个好奇的SQL错误。最后一个查询不起作用。当然，我可以将DELETE分成三个查询，但我真的很想知道MySQL为什么不让我这样做。

一个小例子：

(SELECT id FROM stairs WHERE building = 123)
UNION
(SELECT id FROM lift WHERE building = 123)
UNION
(SELECT id FROM qrcodeid WHERE building = 123)

作品！

DELETE FROM startpoint WHERE id IN (SELECT id FROM stairs WHERE building = 123)

也有效！

尽管

DELETE FROM startpoint WHERE id IN (
    (SELECT id FROM stairs WHERE building = 123)
    UNION
    (SELECT id FROM lift WHERE building = 123)
    UNION
    (SELECT id FROM qrcodeid WHERE building = 123)
)

引发错误

＃1064 - 您的SQL语法出错;检查与MySQL服务器版本对应的手册，以便在UNION（SELECT id FROM lift WHERE building = 123）附近使用正确的语法UNION（SELECT id FROM qrc＆＃39; at line 3

任何人都有线索？

Answer 1

请尝试使用此版本：

DELETE FROM startpoint
    WHERE id IN (select *
                 from ((SELECT id FROM stairs WHERE building = 123)
                       UNION
                      (SELECT id FROM lift WHERE building = 123)
                       UNION
                      (SELECT id FROM qrcodeid WHERE building = 123)
                )

我认为问题是子查询定义的一个神秘问题。子查询是select语句，而union是select语句的组合。

编辑：

实际上，如果你想要效率，你根本不会使用这种方法。我只是想说明如何修复错误。更好的解决方案是：

DELETE sp FROM startpoint sp
    WHERE EXISTS (select 1 from stairs s where s.building = 123 and s.id = sp.id) or
          EXISTS (select 1 from lift l where l.building = 123 and l.id = sp.id) or
          EXISTS (select 1 from qrcodeid q where q.building = 123 and q.id = sp.id);

建议在stairs(id, building)，lift(id, building)和qrcodeid(id, building)上建立索引。

Answer 2

试试那个SQL

DELETE FROM startpoint WHERE id IN (
SELECT id FROM stairs WHERE building = 123
UNION
SELECT id FROM lift WHERE building = 123
UNION
SELECT id FROM qrcodeid WHERE building = 123)

MySQL通过IN条件使用UNION子查询删除FROM

2 个答案: