Question

我有表A和B.表B的项目也可能存在于表A中，我想删除这些项目。这样做的SQL语句会是什么样的？

Answer 1

这是一个选项

delete from a
where a.key in (select key from b)

Answer 2

或者：

DELETE a
WHERE a.some_field IN (SELECT some_field FROM b)

或

DELETE A
WHERE EXISTS (SELECT 1 FROM b WHERE b.field1 = a.field2)

根据您的数据库，您可能会发现其中一个比另一个更好。 IIRC Oracle倾向于选择WHERE EXISTS IN，但这可能取决于许多因素。

Answer 3

类似的东西：

DELETE 
FROM TableA as A 
WHERE A.ID IN (SELECT ID 
               FROM TableB AS B 
               WHERE [your condition here])

Answer 4

在某些数据库中，相当奇特的DELETE FROM FROM是非常高效

delete from foo from foo as f
where exists 
(
  select 1 from bar as b  where b.field = f.field
)

Answer 5

如果您的表使用InnoDB，最简单的方法是使用表B中的foreign keys设置表A，并使用ON DELETE CASCADE。这样就不需要更改代码，并且可以保证数据库的完整性。

Answer 6

根据标准允许这样做。

delete a from a join b on a.id = b.id;

Answer 7

delete a
--select a.*
from tablea a
join tableb b on a.someid = b.someid

确保首先运行选择部分，以确保获得所需的记录。

Answer 8

DELETE FROM FIRST_TABLE FT
WHERE EXISTS(
            SELECT 1
            FROM SECOND_TABLE ST
            WHERE ST.PRIMARY_KEY = FT.PRIMARY_KEY
            );

如何删除一个表中存在的项目？

8 个答案: