差異查詢

Question

的2列的我有一個VoteQuestion表：VoteQuestion(idUser → User, idQuestion → Content, isUp)

和Question表：Question(idQuestion → Content, title)

我要選擇的5個問題的最佳成績（upvotes-downvotes）。
向上投票是VoteQuestion與isUp = TRUE和downvote a VoteQuestion與isUp = FALSE。

我嘗試了以下查詢，但這不是我正在尋找的。它爲每個問題提供相同的分數。

WITH upvotes AS 
( 
    SELECT COUNT(*) AS "a" 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS TRUE 
), 
downvotes AS 
( 
    SELECT COUNT(*) AS "b" 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS FALSE 
) 
SELECT "title", "Question"."idQuestion", upvotes."a"-downvotes."b" AS total 
FROM "VoteQuestion", "Question", upvotes, downvotes 
WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
GROUP BY "title", "Question"."idQuestion", upvotes."a", downvotes."b" 
ORDER BY "total" DESC 
LIMIT 5 

也試過這樣：

SELECT "title", "Question"."idQuestion", 
(SELECT COUNT(*) 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS TRUE 
) AS upvotes, 
(SELECT COUNT(*) 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS FALSE 
) AS downvotes, upvotes-downvotes AS total 
FROM "VoteQuestion", "Question" 
WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
GROUP BY "title", "Question"."idQuestion" 
ORDER BY total DESC 
LIMIT 5 

但它說ERROR: column "upvotes" does not exist

我怎樣才能得到來自查詢的列upvotes和downvotes的區別？

Answer 1

隨着條件語句內嵌到您的True轉換和（分別爲1和-1）爲數字，你可以簡單地總結一下票是這樣的：

SELECT 
    q."title", 
    q."idQuestion", 
    sum(
     case 
      when v."isUp" then 1 
      else -1 
     end 
    ) AS total 

FROM 
    VoteQuestion v join Question q on v."idQuestion" = q."idQuestion" 

GROUP BY 
    q."title", 
    q."idQuestion" 

ORDER BY 
    3 DESC 

LIMIT 5 

我還沒有嘗試過，但我敢肯定，這個工程。

編輯： 下面是其成功運行的SQLFiddle：http://sqlfiddle.com/#!15/df4ca/3

Answer 2

試試這個：

SELECT "title", "Question"."idQuestion", 
(SELECT COUNT(*) as upvotes 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS TRUE 
) AS upvt, 
(SELECT COUNT(*) as downvotes 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS FALSE 
) AS downvt, upvt.upvotes-downvt.downvotes AS total 
FROM "VoteQuestion", "Question" 
WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
GROUP BY "title", "Question"."idQuestion" 
ORDER BY total DESC 
LIMIT 5 

希望它可以幫助你

UPDATE

讓我們試試這個：

SELECT "title", "Question"."idQuestion", 
upvotes, downvotes, upvotes-downvotes AS total 
FROM "VoteQuestion", "Question", 
(SELECT "idQuestion", COUNT(*) as upvotes 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS TRUE GROUP BY "idQuestion" 
) AS upvt, 
(SELECT "idQuestion", COUNT(*) as downvotes 
    FROM "VoteQuestion", "Question" 
    WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
    AND "VoteQuestion"."isUp" IS FALSE GROUP BY "idQuestion" 
) AS downvt 
WHERE "VoteQuestion"."idQuestion" = "Question"."idQuestion" 
AND "VoteQuestion"."idQuestion" = downvt."idQuestion" 
AND "VoteQuestion"."idQuestion" = upvt."idQuestion" 
GROUP BY "title", "Question"."idQuestion" 
ORDER BY total DESC 
LIMIT 5