Question

我正在从斯坦福DB课程中解决问题并提出问题。我有2张桌子。第一个表有2个字段，所以我们有T1（ID1，ID2）。第二个表有更多列。

如果我这样做

select T1.ID1, T1.ID2
from T1, T2 as X, T2 as Y, T2 as Z
where <condition>
except
select T1.ID2, T1.ID1
from T1, T2 as X, T2 as Y, T2 as Z
where <different condition>;

然后我得到2个元组

A1 | B1
A2 | B2

结果是

。这正是我所期待的。

问题是如何使用这些元组从T1中删除行？

我试过

delete
from T1
where ID1=(<select from above using only the first variable in the select>)
  and ID2=(<select from above using only the second variable in the select>);

这不起作用，我没有办法做到这一点。有线索吗？感谢

Answer 1

DELETE FROM t1
inner join T2 ON t1.ID1 = t2.ID1 AND t1.ID2 = t2.ID2

Answer 2

不确定这是否可以在SQLite中使用，但您可以尝试一下：

DELETE FROM T1
WHERE EXISTS (
  SELECT *
  FROM (
    select T1.ID1, T1.ID2
    from T1, T2 as X, T2 as Y, T2 as Z
    where <condition>
    except
    select T1.ID2, T1.ID1
    from T1, T2 as X, T2 as Y, T2 as Z
    where <different condition>
  ) s
  WHERE s.ID1 = T1.ID1
    AND s.ID2 = T1.ID2
)

这可能是次优的，也许你可以改为拆分你的EXCEPT查询：

DELETE FROM T1
WHERE EXISTS (
  /* slightly modified left part of the EXCEPT query */
  select T1.ID1, T1.ID2
  from T1 AS T1_, T2 as X, T2 as Y, T2 as Z
  where <condition>
    AND T1_.ID1 = T1.ID1
    AND T1_.ID2 = T1.ID2
)
AND NOT EXISTS (
  /* slightly modified right part of the EXCEPT query */
  select T1.ID2, T1.ID1
  from T1 AS T1_, T2 as X, T2 as Y, T2 as Z
  where <different condition>
    AND T1_.ID2 = T1.ID1
    AND T1_.ID1 = T1.ID2
)

如何使用另一个表从一个表中删除？

2 个答案: