我知道这个问题与这个问题非常相似：
Symmetric cross join
而且这个也是：
combinations (not permutations) from cross join in sql
Symmetric cross join
而且这个也是：
combinations (not permutations) from cross join in sql
但是,如果我们有两个不同的表,比如说A和B：
select A.id,B.id from A cross join B
我想考虑(a,b)对(b,a)？
解决方法
select A.id aid,B.id bid from A inner join B on a.id <= b.id union select B.id,A.id from A inner join B on b.id < a.id
如果你想变得更复杂：
select distinct
case when a.id<=b.id then a.id else b.id end id1,case when a.id<=b.id then b.id else a.id end id2
from A cross join B
在我用小桌子烘烤的小不科学中,后者更快.在下面,将表达式表达式写为子查询.
select distinct
(select MIN(id) from (select a.id union select b.id)[ ]) id1,(select MAX(id) from (select a.id union select b.id)[ ]) id2
from A cross join B