Question

MySQL表是这样的（VoteID是PK）：

VoteID  VoteValue CommentID
1         -1         1
2         -1         1
3          1         1
4         -1         1
5          1         2
6          1         2
7         -1         2

我需要一个结果：

CommentID    Plus    Minus
    1          1      3 
    2          2      1

“加号”的总和，由CommentID组成的“减号”的总和是否可以在一个SQL表达式中获得所需？

Answer 1

SELECT 
    CommentID,
    SUM(CASE WHEN VoteValue > 0 THEN 1 ELSE 0 END) AS PLUS,
    SUM(CASE WHEN VoteValue < 0 THEN 1 ELSE 0 END) AS MINUS

FROM 
    mytable

GROUP BY 
    CommentID

Answer 2

您需要查询以下行：

SELECT CommentID,
    SUM(IF(VoteValue > 0, 1, 0)) AS Plus,
    SUM(IF(VoteValue < 0, 1, 0)) AS Minus
FROM yourTable
GROUP BY CommentID
ORDER BY CommentID

MySQL GROUP BY数量

2 个答案: