php - 计算单个查询中另一个表的行数

Question

我目前有以下查询从表 posts 中获取帖子。

$stmt = $db->prepare(
"SELECT p_id,p_title,p_date,p_userid,p_world,p_views,p_thumb,p_link,u_username
FROM posts
INNER JOIN users
ON u_id = p_userid
ORDER BY p_hotness DESC
LIMIT 50");
$stmt->execute();
$stmt->bind_result($p_id,$p_title,$p_date,$p_userid,$p_world,$p_views,$p_thumb,$p_link,$u_username);
while($stmt->fetch()){
  $posts[] = [
    'p_id' => $p_id,
    'p_title' => $p_title,
    'p_date' => $p_date,
    'p_userid' => $p_userid,
    'p_world' => $p_world,
    'p_views' => $p_views,
    'p_thumb' => $p_thumb,
    'p_link' => $p_link,
    'u_username' => $u_username
  ];
};
$stmt->close();

不过，我还想从另一个表 post_votes 中获取帖子的赞成票和反对票数量，该表包含以下列:

pv_id | pv_ip | pv_type | pv_postid | pv_userid

pv_type 是 0(反对票)或 1(赞成票)。

SELECT COUNT(*) FROM post_votes WHERE pv_postid = ? AND pv_type = 1 // upvotes
SELECT COUNT(*) FROM post_votes WHERE pv_postid = ? AND pv_type = 0 // downvotes

目前，我可以将此 SQL 放在显示每个帖子的 foreach 循环中，但这样做效率很低，因为它在循环的每次迭代中执行多个查询。

有什么方法可以计算上面第一个查询中帖子的赞成票和反对票数量？

Answer 1

试试这个查询

SELECT p_id,p_title,p_date,p_userid,p_world,p_views,p_thumb,p_link,u_username,
sum(IF( pv.pv_type=  '1', 1 ,  0 ))  as upvote, sum(IF( pv.pv_type=  '0', 1 ,  0 ))  as downvote
FROM posts INNER JOIN users ON u_id = p_userid 
JOIN post_votes pv ON pv.pv_postid = posts.p_id 
ORDER BY p_hotness DESC
LIMIT 50

并针对未投票和有投票尝试此查询

SELECT p_id,p_title,p_date,p_userid,p_world,p_views,p_thumb,p_link,u_username,
(select sum(IF( pv.pv_type=  '1', 1 ,  0 )) from post_votes pv where pv_postid=posts.p_id ) as upvote,(select sum(IF( pv.pv_type=  '0', 1 ,  0 )) from post_votes pv where pv_postid=posts.p_id ) as downvote 
FROM posts INNER JOIN users ON u_id = p_userid  ORDER BY p_hotness DESC LIMIT 50