Question

我有一个评级表，用于存储用户ID，对象ID和分数（+1或-1）。现在，当我想显示一个对象列表，其总分，+1票数和-1票数。

如何有效地执行此操作而无需执行SELECT COUNT（*）FROM rating WHERE（score = +/- 1 AND object_id = ..）？这是每个对象显示的两个查询，这是不可接受的。数据库设计合理吗？

Answer 1

虽然它没有解决您的合理设计问题，但这里有一个查询可以同时为您提供两个计数：

select
    sum(case when score = 1 then 1 else 0 end) 'positive'
,   sum(case when score = -1 then 1 else 0 end) 'negative'
,   objectId
from
    ratings
where
    objectId = @objectId ...
group by
    objectId

Answer 2

select object_id, 
       sum(case when score = 1 then 1 else 0) upvotes, 
       sum(case when score = -1 then -1 else 0) downvotes,
       sum(score)
from ratings
group by object_id

也许就是这样。

Answer 3

这应该这样做：

SELECT
    UserID, ObjectID,
    SUM(CASE WHEN score=1 Then 1 Else 0 End) as UpVotes,
    SUM(CASE WHEN score=-1 Then 1 Else 0 End) as DownVotes,
FROM YourTable
GROUP BY UserID, ObjectID

最佳查询评级数据库？

3 个答案: