Question

这是一个没有问题的MySql 5.0.51执行的查询：

SELECT cc_split.idSplit,
       count( voteup.vote),
       count( votedown.vote)
FROM cc_split
LEFT JOIN cc_split_usager AS voteup ON voteup.idSplit = cc_split.idSplit
      AND voteup.vote >0
LEFT JOIN cc_split_usager AS votedown ON votedown.idSplit = cc_split.idSplit
      AND votedown.vote <0
WHERE cc_split.isArchived = false
GROUP BY cc_split.idSplit
LIMIT 0, 30

问题在于COUNT没有显示我想要的内容。您是否可以看到，它需要cc_ split_ usager并且应该计算正数的投票数量，另一方面计算负数的投票数量。上面的代码显示数字2 upvote和2 downvote实际上它应该是2 upvote和1 downvote。在单个SQL查询中有什么技巧可以使用upvote和downvote的数量。

表格如下：

cc_split:
-idSplit
-...
cc_split_usager:
-idSplit
-vote (can be +1 or -1)
-...

对我有任何暗示吗？

Answer 1

尝试：

SELECT s.idSplit, 
    count(case when v.vote > 0 then 1 else null end) as VoteUp, 
    count(case when v.vote < 0 then 1 else null end) as VoteDown 
FROM cc_split s
LEFT JOIN cc_split_usager AS v ON v.idSplit = s.idSplit
WHERE s.isArchived = false
GROUP BY s.idSplit
LIMIT 0, 30

Answer 2

试试这个：

SELECT s.idSplit, 
    Sum( Case When vote > 0 Then 1 Else 0 End) UpVotes,
    Sum( Case When vote < 0 Then 1 Else 0 End) DownVotes
FROM cc_split s       
   LEFT JOIN cc_split_usager v 
      ON v.idSplit = s.idSplit        
WHERE s.isArchived = false        
GROUP BY s.idSplit        
LIMIT 0 , 30

具有2个分组的SQL查询

2 个答案: