Question

我有MySQL查询，我认为需要子查询。我想计算每条评论中“向上”投票的总数，并确定某个用户是否已对每条评论进行投票：

以下是我的表格：

Comments Table:
  comment_id  comment      acct_id     topic_id    comment_date
      5        hello5        2             1            9:00am
      7        hello7        3             1           10:00am

  Votes Table:
  comment_id   vote        acct_id     topic_id
     5          1             1            1
     7          1             4            1
     5          1             5            1

这是我得到的输出：

  comment_id  commenter  comment  voter   sum    did_i_vote 
      5           2      hello5     1      2          1 
      7           3      hello7     4      1          1

这是所需的输出：

  comment_id  commenter  comment  voter   sum    did_i_vote 
      5           2      hello5   **5**    2          1 
      7           3      hello7     4      1          1

这是我的疑问：

SELECT votes.acct_id as voter, comments.comment_id, comment, comments.acct_id as 
commenter, SUM(vote) as sum, vote as did_i_vote
from votes 
right join comments 
on votes.comment_id=comments.comment_id 
join accounts on comments.acct_id=accounts.acct_id 
where topic_id=1 
group by comments.comment_id order by comment_date desc

除了voter之外，您会注意到这两个输出是相同的。

我缺少的查询是一种确定给定用户（例如voter=acct_id=5）是否是对任何评论投票的用户的方法。如果没有这个条件，查询会从列表中选择voter comment_id=5为voter=1的第一个SELECT from votes where voter='X'。

所以我的问题是我认为我需要插入以下子查询：

from

我只是不确定在哪里或如何。将它放在上面votes和sum()之间的括号中会消除{{1}}函数，因此我陷入困境。

有什么想法吗？

Answer 1

如果我从上面的评论中正确地理解了你，我认为您需要做的就是（外部）将votes表加入到您的查询中，这次只是在帐户的投票中问题：

SELECT
   comments.comment_id       AS comment_id,
   comments.acct_id          AS commenter,
   comment                   AS comment,
-- votes.acct_id             AS voter,                        -- ambiguous
   SUM(votes.vote)           AS sum,
   my_votes.vote IS NOT NULL AS did_i_vote
FROM
             votes
  RIGHT JOIN comments ON votes.comment_id=comments.comment_id
        JOIN accounts ON comments.acct_id=accounts.acct_id    -- what purpose ?
  LEFT  JOIN votes AS my_votes ON
               my_votes.commentid=comments.comment_id
           AND my_votes.acct_id=@my_acct_id
WHERE topic_id = 1                                            -- ambiguous
GROUP BY comments.comment_id
ORDER BY comment_date DESC

关于评论投票的mysql子查询问题

1 个答案: