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Counting the number of positive and negative votes:

I have the following tables:

post (id, title, content) etc
author (id, username) etc
author_vote (post_id, author_id, value)

The value is tiny_int, which can be 1 or -1.

I want to count the number of positive and negative votes for each message:

$posts = sql_select($link, "SELECT post.*, author.username 
                            FROM post, author 
                            AND author.id = post.author_id");

Why is the following code not working?

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"));
});

I also tried the following: this leads to the fact that all the voices are the same for each message:

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"));
}

Also, is there a way to do this without having to query the database several times for each message? How will something that constantly changes [like this] get (mem) cached?

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2 answers

You can make your account in one request:

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 = ...

:

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

, :

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
+5

sql_select(), , count(*) SQL , sum(). , , . GROUP BY:

SELECT value, count(value) AS value_count FROM author_vote WHERE post_id = $id GROUP BY value

. , .

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