仅在未违反唯一约束时更新表

Question

我有下表：

Id   Account_Number  Csd_id   pk_id  dk_id
1       343          200      100     50
2       234          400      200     70
3       343          400      100     70

我对account_number，csd_id和pk_id有一个独特的约束。

现在，我想将所有csd_id更新为200 csd_id 400，只有在未违反上述唯一约束的情况下才会{。}}。

更新完成后，我必须删除csd_id为400的剩余记录。

Answer 1

您只需要一个包含update子句的not exists语句，以避免违反约束的更新。当然，对于左上行，您需要一个简单的delete语句：

update tbl t1
   set t1.csd_id = 200
 where t1.csd_id = 400
   and not exists (
     select null
       from tbl t2
      where t2.account_number = t1.account_number
        and t2.pk_id = t1.pk_id
        and t2.csd_id = 200
   );

delete tbl where csd_id = 400;

修改

非常不可能，但如果account_number或pk_id都可以为空：

update tbl t1
   set t1.csd_id = 200
 where t1.csd_id = 400
   and not exists (
     select null
       from tbl t2
      where (t2.account_number = t1.account_number or (t2.account_number is null and t1.account_number is null))
        and (t2.pk_id = t1.pk_id or (t2.pk_id is null and t1.pk_id is null))
        and t2.csd_id = 200
   );

delete tbl where csd_id = 400;