MySQL DELETE FROM与IN条件的UNION子查询 [英] MySQL DELETE FROM with UNION subquery by IN condition

问题描述

我遇到了一个奇怪的SQL错误.最后一个查询不起作用.当然，我可以将DELETE分为三个查询，但是我真的很奇怪为什么MySQL不允许我这样做.

I have tripped up on a curious SQL error. The last query doesn't work. Of course I can just split that DELETE into three queries, but I really wonder why MySQL doesn't let me do it this way.

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)

有效！

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

也可以！

而

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语法有错误；请查看与您的MySQL服务器版本相对应的手册，以获取正确的语法，以在第3行的"UNION(SELECT ID from lift WHERE building = 123)UNION(SELECT id FROM qrc)"附近使用

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UNION (SELECT id FROM lift WHERE building = 123) UNION (SELECT id FROM qrc' at line 3

有人知道吗?

推荐答案

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)
                )

我认为该问题是带有子查询定义的奥秘问题.子查询是select语句，而union是select语句的结合.

I think the issue is an arcane issue with the definition of a subquery. A subquery is a select statement, whereas a union is a conjunction of select statements.

实际上，如果您想提高效率，则根本不会使用这种方法.我只是试图显示如何解决该错误.更好的解决方案是:

Actually, if you want efficiency, you wouldn't use this approach at all. I was just trying to show how to fix the error. A better solution would be:

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)上使用索引.

Indexes are recommended on stairs(id, building), lift(id, building), and qrcodeid(id, building).

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