我需要帮助来创建SQL查询

Question

我正在使用asp.net创建一个个人网站，但我对SQL并不熟悉，在创建查询时需要帮助。

我有3个表格，其中包含以下列：

  

UserInfos - UserID，NickName，PictureAva和Privacy   UserFollower - FollowerId，FollowingId，Status。
  PlaceFollower - FollowerId，FollowingId，Date，Status。

我需要从UserInfos表中选择所有人。

标准：

If Privacy = 0, I don't want this Row to be returned.
If Privacy = 1, I need that the rows from UserInfos be returned when 
              UserInfos.UserID = UserFollower.FollowingId 
          and UserFollower.FollowerId = 2 
          and UserFollower.Status = 1, 
          only if PlaceFollower.FollowerId = UserFollower.FollowingId 
              and PlaceFollower.FollowingId = 1 
              and PlaceFollower.Status = 1 
              and PlaceFollower.Date = '17/07/2011'.

    If Privacy = 2, I need that the rows from UserInfos be returned when 
             UserInfos.UserID = UserFollower.FollowingId 
          and UserFollower.FollowerId = 2 
          and UserFollower.Status = 1, 
       **OR** UserInfos.UserID = UserFollower.FollowerId 
          and UserFollower.FollowingId = 2 
          and UserFollower.Status = 1, 
          only if PlaceFollower.FollowerId = UserFollower.FollowingId 
          and PlaceFollower.FollowingId = 1 
          and PlaceFollower.Status = 1 
          and PlaceFollower.Date = '17/07/2011'.

是否可以这样做？

感谢您的帮助。

Answer 1

我会建议UNION。

select .. join .. where privacy=1
UNION ALL
select ..  join .. where privacy=2