Question

我有一张表likes，其中ID1喜欢ID2

ID1     ID2
1025    1101
1247    1468
1316    1304
1501    1934
1641    1468
1689    1709
1709    1689
1782    1709
1911    1247
1934    1501

所以我选择那些喜欢彼此的人，就是这个例子

1501 1934
1934 1501

但我想只选择一对，我无法做到。谁能指出我正确的方向？它是一个更大的查询的一部分，但这部分我无法做到。

由于

Answer 1

要获得所有回复喜欢的明确列表，您可以使用

SELECT ID1,
       ID2
FROM   likes L1
WHERE  ID1 > ID2
       AND EXISTS(SELECT *
                  FROM   likes L2
                  WHERE  L1.ID1 = L2.ID2
                         AND L1.ID2 = L2.ID1)

Answer 2

select
     L1.ID1, L1.ID2
from likes L1
where exists 
     (select 1
      from likes L2
      where L1.ID1 = L2.ID2 and L1.ID2 = L2.ID1)

Answer 3

修复数据：

SELECT ID1, ID2
  FROM likes
 WHERE ID1 < ID2
UNION
SELECT ID2 AS ID1, ID1 AS ID2
  FROM likes
 WHERE ID1 > ID2;

...然后通过向表中添加数据完整性约束来修复泄漏，例如

CREATE TABLE likes 
(
 ID1 INTEGER NOT NULL, 
 ID2 INTEGER NOT NULL, 
 CHECK (ID1 < ID2),
 UNIQUE (ID1, ID2)
);

Answer 4

SELECT L1.ID1, L1.ID2 FROM Likes L1, Likes L2 
WHERE L1.ID1=L2.ID2 AND L1.ID2=L2.ID1 AND L1.ID1>L1.ID2

相互朋友列，只选择一对

4 个答案: