java - 运行复杂查询

Question

我的目标是做两件事： - 计算特定房间中每个
人的数量votes（此表称为votes） 。 - 查明用户 ID 是否至少对一首歌曲投票（在特定房间）songID

和被传递到查询中userID。RoomID我不确定如何“循环”每个songID. 我是否运行两个查询 - 首先获取每个查询songID，然后运行一个for循环来获取上述信息（为此使用 Java）？

Answer 1

您可以针对第一个问题执行此操作

SELECT Count(songID), songID
FROM votes
WHERE RoomID = @roomid
GROUP BY songID

这是第二个问题

SELECT songID
FROM votes
WHERE UserID = @userid
      AND RoomID = @roomid

Answer 2

select SongID, count(*) as voteCount, 
case when exists( 
        select 1 from votes b 
        where b.songID = a.songId and b.RoomID = ? and b.UserID = ? ) 
    then 'Yes' else 'No' end case as didUserVote
from votes a
where a.RoomID = ?
group by SongID

如果这不起作用，试试这个 - 如果用户没有投票给这首歌，第三列将为空，UserID如果他们这样做了。

select a.SongID, count(*) as voteCount, b.UserID
from votes a left join votes b on a.songID = b.songID and b.RoomID = ? and b.UserID = ?
where a.RoomID = ?
group by a.SongID, b.UserID

Answer 3

如果 retunr 为 NULL 则在第三列尝试此操作 没有投票

select SongID, count(*) as voteCount,(
        select b.userid from votes b 
        where b.songID = a.songId and b.RoomID = 131 and b.UserID = 70)
    from votes a
    where a.RoomID = 131
    group by SongID