Question

我有一个跟踪粉丝的表

FollowerUserId, FollowingUserId
1                   2
2                   1
3                   1
4                   1
1                   5

我想让所有给定Id的用户跟随，然后是或者两者。例如对于UserId 1，我希望结果为：（FG：关注，FD：关注，B：两种方式）

2,B
5,FG
3,FD
4,FD

我可以通过联盟轻松获得FG和FD

Select FollowerUserId, 'FD' From Table Where FollowingUserId =1
Union
Select FollowingUserId, 'FG' From Table Where FollowerUserId =1;

以上我将用户2作为

2,FG 
2,FD

从上面但我真的需要2，B 没有UserId 2重复。如何有效地完成这项工作？

Answer 1

您可以在基本查询中使用聚合：

SELECT UserId,
       (CASE WHEN COUNT(DISTINCT which) = 1 THEN MIN(which)
             ELSE 'B'
        END)
FROM (Select FollowerUserId as UserId, 'FD' as which From Table Where FollowingUserId = 1
      Union ALL
      Select FollowingUserId, 'FG' From Table Where FollowerUserId = 1
     ) f
GROUP BY UserId;

从一个列表中的表中获取关注者和FollwedBy用户

1 个答案: