通过 IN 条件使用 UNION 子查询的 MySQL DELETE FROM答案

【问题标题】：MySQL DELETE FROM with UNION subquery by IN condition通过 IN 条件使用 UNION 子查询的 MySQL DELETE FROM
【发布时间】：2013-06-17 23:38:36
【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。当然我可以把那个 DELETE 分成三个查询，但是我真的很奇怪为什么 MySQL 不允许我这样做。

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)

有效！

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

也有效！

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；检查与您的 MySQL 服务器版本相对应的手册，以在第 3 行的“UNION (SELECT id FROM lift WHERE building = 123) UNION (SELECT id FROM qrc”附近使用正确的语法

有人知道吗？

【问题讨论】：

标签： mysql subquery union sql-delete in-subquery

【解决方案1】：

试试这个版本：

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)
                )

我认为这个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 语句的结合。

编辑：

实际上，如果您想要效率，您根本不会使用这种方法。我只是想展示如何修复错误。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) 上使用索引。

【讨论】：

这行得通（一旦 SQL 错误被修复 - 请参阅我的编辑）。它不如 rkpasia 的解决方案高效，但它适用于联合成员上需要括号的情况，例如在子查询上使用 LIMIT 时。

【解决方案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)

【讨论】：

如您所见，没有括号！