MYSQL GROUP BY 具有特定列的多个不同值

Question

MYSQL 结构:

 ID | USERID | FRIENDID | Type
-------------------------------
 1  |   10   |    20    | Gold
 2  |   20   |    10    | Gold

 3  |   30   |    40    | Silver
 4  |   40   |    30    | Silver

 5  |   50   |    60    | Gold
 6  |   60   |    50    | Gold

 7  |   70   |    80    | Bronze
 8  |   80   |    70    | Bronze

 9  |   90   |   100    | Bronze
10  |  100   |    90    | Bronze

我想要的是 GROUP (ID 1 & ID 2) 和 (ID 5 & ID 6)，因为它们是“黄金”类型，不是按类型分组。

返回结果:

 1. 10 & 20, type:gold. (GROUP)

 3. 30 & 40, type:silver.
 4. 40 & 30, type:silver.

 5. 50 & 60, type:gold. (GROUP)

 7. 70 & 80, type:bronze.
 8. 80 & 70, type:bronze.

 9. 90 & 100, type:bronze.
10. 100 & 90, type:bronze.

如何使用 php 查询来做到这一点？

演示:http://sqlfiddle.com/#!2/13bd3/1

Answer 1

您需要做的是根据类型添加额外的分组子句。当它是“黄金”时，你会得到一个常数。否则，您使用 id:

select least(userid, friendid), greatest(userid, friendid), type
from t
group by least(userid, friendid), greatest(userid, friendid),
         (case when type = 'gold' then 0 else id end)

这确实重新排列了非黄金类型的 id 的顺序。如果顺序很重要，则 SQL 稍微复杂一些:

select (case when type = 'gold' then least(userid, friendid) else userid end),
       (case when type = 'gold' then greatest(userid, friendid) else friendid end),
       type
from t
group by least(userid, friendid), greatest(userid, friendid),
         (case when type = 'gold' then 0 else id end)