select 每个 post php mysql 的反对票和赞成票

Question

我有一个论坛，用户可以在其中 post 提问，也可以投赞成票和反对票。

我想获取每个 post 的 upvote 和 downvote。

我之前所做的是在 3 组查询中执行此操作。

$data = mysqli_query($con,"select * from posts");
while($row = mysqli_fetch_assoc($data)){
  $pid  = $row['post_id'];
  $up = mysqli_fetch_assoc(mysqli_query("SELECT COUNT(*) as c FROM up WHERE post_id = $pid"))['c'];
  $down = mysqli_fetch_assoc(mysqli_query("SELECT COUNT(*) as c FROM down WHERE post_id = $pid"))['c'];
}

任何人都可以告诉我如何在 一个查询 中做这些事情，因为如果在第一个查询中得到很多 posts 那么就会有很多要做的查询。

Answer 1

你可以为此使用相关子查询 where upvotes 并且根据 post id

计算反对票数

SELECT p.*,
       ( select count(*)  from up where post_id = p.post_id ) as upVotesCount,
       ( select count(*)  from down where post_id = p.post_id ) as downVotesCount,
 FROM posts p

Answer 2

您可以使用子查询并将所有内容放在第一个查询中。

这可能是一个好的开始:

$data = mysqli_query($con, "select posts.*, " . 
                           "(SELECT COUNT(*) FROM up WHERE post_id = posts.post_id) as totalUp, " . 
                           "(SELECT COUNT(*) FROM down WHERE post_id = posts.post_id) as totalDown " .
                           "from posts");
while($row = mysqli_fetch_assoc($data)){
  // ...
}

select 每个 post php mysql 的反对票和赞成票

select down and up votes for each post php mysql

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