2列查询的差异

Question

我有一个VoteQuestion 表：VoteQuestion(idUser → User, idQuestion → Content, isUp)

还有一个Question 表：Question(idQuestion → Content, title)

我想选择得分最高的 5 个问题（赞成-反对）。
赞成票是VoteQuestion 和isUp = TRUE，反对票是VoteQuestion 和isUp = FALSE。

我尝试了以下查询，但这不是我想要的。它对每个问题给出相同的分数。

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

也试过这个：

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

但上面写着ERROR: column "upvotes" does not exist

如何从查询中获取某一列中赞成票和反对票的区别？

Answer 1

使用内联条件语句将您的 True 和 False 值转换为数字（分别为 1 和 -1），您可以像这样简单地总结投票：

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

我还没有尝试过，但我很确定这可行。

编辑： 这是成功运行的 SQLFiddle：http://sqlfiddle.com/#!15/df4ca/3

Answer 2

试试这个：

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

希望对你有帮助

更新

让我们试试这个：

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