SQL與交叉值配對的行

Question

我想在表中配對兩行。

 
ZZ XX PZZ PXX 
A B 1 2 
G E 5 9 
M N 4 4 
E H 7 4 
Q R 2 2 
T D 8 1 
H E 4 7 
B A 2 1 
L B 7 3 

我想配對行具有相同的值，但值交叉到其他列如下。 預期輸出：

 
ZZ XX PZZ PXX 
A B 1 2 
B A 2 1 
E H 7 4 
H E 4 7 

Answer 1

一個簡單INNER JOIN將做：

SELECT t1.ZZ, t1.XX, t1.PZZ, t1.PXX 
FROM mytable AS t1 
INNER JOIN mytable AS t2 
ON t1.ZZ = t2.XX AND t1.XX = t2.ZZ AND t1.PZZ = t2.PXX AND t1.PXX = t2.PZZ 

ON的條款做XX，ZZ之間PXX，PZZ列F中的表之間的交叉匹配。

Demo here

Answer 2

使用一個EXISTS子句來檢查，如果存在兄弟姐妹。

select * 
from mytable 
where exists 
(
    select * 
    from mytable pair 
    where pair.zz = mytable.xx 
    and pair.xx = mytable.zz 
    and pair.pzz = mytable.pxx 
    and pair.pxx = mytable.pzz 
); 

或甚至IN子句簡單：

select * 
from mytable 
where (zz, xx, pzz, pxx) in 
(
    select xx, zz, pxx, pzz 
    from mytable 
); 

如果你想你的結果排序，使用ORDER BY以最少和最偉大：

order by least(xx, zz), greatest(xx, zz), zz, least(pxx, pzz), greatest(pxx, pzz), pzz;