Question

我有一个论坛，用户可以发布问题，并可以进行投票和投票。

我希望得到每个帖子的upvote和downvote。

我之前做的是在3组查询中做到这一点。

$data = mysqli_query($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单个查询中执行这些操作，因为如果在第一个查询中获得了大量posts，则会有很多查询要执行。< / p>

Answer 1

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)){
  // ...
}

Answer 2

你可以使用相关子查询来获得upvotes 和downvotes根据帖子ID计算

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

为每个帖子php mysql选择向下和向上投票

2 个答案: