Question

如果没有主键或外键，是否可以删除表B中存在的表A中的所有记录？与this answer类似：

DELETE a 
FROM @A a
WHERE EXISTS (SELECT a.* INTERSECT SELECT * FROM @B)

在DB2中，每个SELECT都必须有一个FROM子句，而FROM sysibm.sysdummy1在这里不起作用。

Answer 1

就个人而言，我可能只是使用一个多步骤的过程......

create table tmp as (
select * from @A
EXCEPT
select * from @B
);

delete from @A;

insert into @A
 select * from tmp;

我能想到的任何其他内容似乎都需要明确的列名列表。

delete 
from @A a
where exists (select *
              from @B b
              where a.Fld1 = b.Fld1
                   and a.Fld2 = b.Fld2
                  <...>
             );

也被认为是量化的谓词和IN谓词......类似于

delete 
from @A a
where (a.*) in (select * from @B);

delete 
from @A a
where (a.*) <> ALL (select * from @B);

但我不相信（a。*）被认为是行值表达式，无论两者的文档都说

全选
的最外层选择列表中不允许使用SELECT *

最后，请注意，如果有任何 NULL 列，所有这些都会出现问题。

Answer 2

尝试这样的事情：

delete from @A a
where exists 
(
 select * from @b b
 where 
 (b.field1=a.field1 or b.field1 is null and a.field1 is null) and  
 (b.field2=a.field2 or b.field2 is null and a.field2 is null) and  
 (b.field3=a.field3 or b.field3 is null and a.field3 is null)   
)

在DB2中使用INTERSECT进行DELETE

2 个答案: