类似 Stackoverflow 的评论投票 SQL 查询

Question

我正在开发一个评论系统，例如 Stackoverflow 或 Disqus，人们可以在其中对 cme​​ts 进行评论和投票。我为此准备了三个表：USERS、COMMENTS 和 VOTES。

我无法弄清楚如何编写查询来计算投票并返回给定用户是否投票。每个用户每条评论只能投票一次，不能对自己的评论投票。此外，cmets 和投票不只是针对一个主题。每个页面都有自己的主题，因此在对 SELECT 进行 GET 和投票时，WHERE topic_id='X' 也需要反映在查询中。

这是我的表的数据，到目前为止我的查询看起来如何，以及我希望它返回什么：

USERS table
user_id user_name   
 1         tim
 2         sue
 3         bill 
 4         karen
 5         ed

COMMENTS table
comment_id topic_id    comment   commenter_id
 1            1       good job!         1
 2            2       nice work         2
 3            1       bad job :)        3

VOTES table
 vote_id    vote  comment_id  voter_id
  1          -1       1          5
  2           1       1          4
  3           1       3          1
  4          -1       2          5
  5           1       2          4

SELECT users.*, comments.*, count(vote as totals), sum(vote=1 as yes), sum(vote=-1 as no),
my_votes.vote as did_i_vote, users.* as IM_THE_USER
from comments
join votes 
on comments.comment_id=votes.comment_id
join users
on comments.commenter_id=users.user_id
join votes as MY_votes
on MY_votes.voter_id=IM_THE_USER.user_id
where topic_id=1 and IM_THE_USER.user_id=1
group by comment_id

user_id user_name comment_id topic_id  comment   commenter_id  totals yes no did_i_vote
   1      tim          1        1      good job!     1           2     1   1    NULL  
   3      bill         3        1      bad job:)     3           1     1   0      1

Answer 1

SQL Fiddle 玩

select u.user_id, u.user_name,
       c.comment_id, c.topic_id,
       sum(v.vote) as totals, sum(v.vote > 0) as yes, sum(v.vote < 0) as no,
       my_votes.vote as did_i_vote
from comments c
join users u on u.user_id = c.commenter_id
left join votes v on v.comment_id = c.comment_id
left join votes my_votes on my_votes.comment_id = c.comment_id
                            and my_votes.voter_id = 1
where c.topic_id = 1
group by c.comment_id, u.user_name, c.comment_id, c.topic_id, did_i_vote;

更新：固定 group by 子句

由 OP (tim peterson) 更新：将计数固定为总数并添加评论本身以由查询返回 final working SQLFiddle