如何列出多個領域從單一的表在Oracle SQL匹配

Question

我有如下表：

create table Likes(ID1 number(5), ID2 number(5)); 
insert into Likes values(1689, 1709); 
insert into Likes values(1709, 1689); 
insert into Likes values(1782, 1709); 
insert into Likes values(1911, 1247); 
insert into Likes values(1247, 1468); 
insert into Likes values(1641, 1468); 
insert into Likes values(1316, 1304); 
insert into Likes values(1501, 1934); 
insert into Likes values(1934, 1501); 
insert into Likes values(1025, 1101); 

表包含了由它們的ID識別用戶的「喜歡」。喜歡是單向連接（如果ID1喜歡ID2並不意味着TD2喜歡ID1）。

我想找到這些ID，其中是雙向連接（其中'liker'是'喜歡'，由用戶喜歡）。

我是初學者與Oracle SQL，我希望我的問題是不是平庸......

Answer 1

你可以做一個連接：

SELECT t.id1,t.id2 
FROM Likes t 
INNER JOIN Likes s 
ON(t.id1 = s.id2 and t.id2 = s.id1) 

或用EXISTS（）

SELECT t.* 
FROM Likes t 
WHERE EXISTS(select 1 FROM Likes s 
      WHERE t.id1 = s.id2 
       AND t.id2 = s.id1) 

Answer 2

只有在表中存在其他記錄的情況下，您需要選擇給定的記錄id1 = X，id2 = Y，
其中id1 = Y，id2 = X。
像這樣的情況可以在SQL中表示與EXISTS操作和相關子查詢的幫助：

SELECT * 
FROM likes t 
WHERE EXISTS (
    SELECT 1 FROM likes t1 
    WHERE t.id1 = t1.id2 AND t.id2 = t1.id1 
) 

Answer 3

試試這個：

with tab as (select id1, id2 from Likes) 
select id1, id2 from tab 
intersect 
select id2, id1 from tab; 

應該有更好的表現，原因是其會閱讀Likes表只有一次

Answer 4

使用此查詢：

 SELECT 
      id1, id2 from Likes L1 
     INNER JOIN (
      Select id1, id2 from Likes 
     ) as L2 
     on (L1.id1 = L2.id) 
WHERE L1.id2 = L2.id1