我有以下表格:
post (id, title, content) etc
author (id, username) etc
author_vote (post_id, author_id, value)
值是一个tiny_int,可以是1或-1。
我想计算每个帖子的正面和负面投票数量:
$posts = sql_select($link, "SELECT post.*, author.username
FROM post, author
AND author.id = post.author_id");
为什么以下代码不起作用?
array_walk($posts, function(&$post, $link){
$post['positive'] = sql_select($link, "SELECT SUM(value) FROM author_vote WHERE post_id = $post['id']
AND value = 1");
$post['negative'] = abs(sql_select($link, "SELECT SUM(value) FROM author_vote WHERE post_id = $post['id']
AND value = -1"));
});
我也尝试过以下操作,这会导致每个帖子的所有投票都相同:
foreach ($posts as &$post)
{
$id = $post['id'];
$post['positive'] = (int)sql_select($link, "SELECT SUM(value) FROM author_vote WHERE post_id = $id
AND value = 1");
$post['negative'] = (int)abs(sql_select($link, "SELECT SUM(value) FROM author_vote WHERE post_id = $id
AND value = -1"));
}
还有什么方法可以做到这一点,而不必为每个帖子多次查询数据库?如何(像这样)不断变化的东西(缓存)是什么?
答案 0 :(得分:5)
您可以在一个查询中进行计数:
Select Sum( Case When value < 0 Then 1 Else 0 End ) As NegVotes
, Sum( Case When value > 0 Then 1 Else 0 End ) As PosVotes
From author_vote
Where post_id = ...
如果你想要每个帖子的正面和负面投票:
Select post_id
, Sum( Case When value < 0 Then 1 Else 0 End ) As NegVotes
, Sum( Case When value > 0 Then 1 Else 0 End ) As PosVotes
From author_vote
Group By post_id
如果您想要合并第一个查询和第二个查询,可以获得:
Select post....
, author.username
, Coalesce(post_count.NegVotes,0) As NegVotes
, Coalesce(post_count.PosVotes,0) As PosVotes
From post
Join author
On author.id = post.author_id
Left Join (
Select post_id
, Sum( Case When value < 0 Then 1 Else 0 End ) As NegVotes
, Sum( Case When value > 0 Then 1 Else 0 End ) As PosVotes
From author_vote
Group By post_id
) As post_count
On post_count.post_id = post.post_id
答案 1 :(得分:0)
我找不到您正在使用的函数sql_select()
,但您可能最好在SQL中使用count(*)
而不是尝试sum()
。您只需计算它看起来的行,而不是对值求和。你也可以得到一点点发烧友并使用GROUP BY:
SELECT value, count(value) AS value_count FROM author_vote WHERE post_id = $id GROUP BY value
这将为每个唯一值返回一行。返回的每一行都将使用该值报告唯一值和行数。