最佳查詢收視率數據庫？

Question

我有一張存儲用戶ID，對象ID和分數（+1或-1）的評分表。現在，當我想顯示一個對象列表，其總分數，+1票數和-1票數。

我怎樣纔能有效地做到這一點，而不必做SELECT COUNT（*）FROM評分WHERE（score = +/- 1 AND object_id = ..）？這是每個對象顯示的兩個查詢，這是不可接受的。數據庫設計是否合理？

Answer 1

雖然它並沒有解決您的合理設計問題，這裏，讓你一次這兩個方面的查詢：

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 

也許類似的東西。

Answer 3

這應做到：

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