Mysql 2列数据分组

Question

我有一张 table :

id a b
1 1 2
2 2 1
3 2 1
4 3 2
5 2 3

col a b [1 2] 等于 col a b [2 1]，所以我想将这些数据分组，我怎样才能得到如下结果:

id a b
5 2 3
3 2 1

谢谢。

Answer 1

SELECT *
FROM   TableName
WHERE  (LEAST(a, b), GREATEST(a, b), id) in 
(
    SELECT  LEAST(a, b) as x, 
            GREATEST(a, b) as y, 
            MAX(ID) as id
    FROM    TableName 
    GROUP   BY x, y
)

• SQLFiddle Demo