一次SQL查询中的多次计数

Question

我正在用CodeIgniter构建一个Web应用程序。

用户可以“爱”或“讨厌”帖子。这些行动都存储在一个表中调用与下面的列post_rating：

• ID
• POST_ID
• USER_ID
• 评级

评级可以是0中性，1为爱或2仇恨。

在我的模型，我已经回到了各自岗位具有以下功能的一些基本信息：

function get_posts($thread_id) 

{ 

    $this->db->select('id, user_id, date_posted, content'); 
    $this->db->from('post'); 
    $query = $this->db->get(); 

    if ($query->num_rows() > 0) 

    { 

     return $query->result(); 

    } 

} 

我明白我需要加入post_rating表，但我怎么会去还回的爱和讨厌与标题，内容等在同一阵列中计数？

谢谢！

:)

更新！

这是我此刻的MODEL：

function get_posts($thread_id) 

{ 

    $this->db->select('post.id, post.user_id, post.date_posted, post.content, post.status_visible, user.username, user.location, user.psn, user.clan, user.critic, user.pro, SUM(case when rating = 1 then 1 end) as love, SUM(case when rating = 2 then 1 end) as hate'); 
    $this->db->from('post'); 
    $this->db->join('user', 'user.id = post.user_id', 'left'); 
    $this->db->join('post_rating', 'post_rating.post_id = post.id', 'left'); 
    $this->db->where('thread_id', $thread_id); 
    $this->db->order_by('date_posted', 'asc'); 
    $query = $this->db->get(); 

    if ($query->num_rows() > 0) 

    { 

     $this->db->select('id'); 
     $this->db->from('post_vote'); 

     return $query->result(); 

    } 

} 

Answer 1

可以使用case总结两个不同的统计：

select title 
,  content 
,  sum(case when pr.rating = 1 then 1 end) as Love 
,  sum(case when pr.rating = 2 then 1 end) as Hate 
,  (
     select count(*) 
     from posts up 
     where up.user_id = p.user_id 
     ) as UserPostCount 
from posts p 
left join 
     posts_rating pr 
on  pr.post_id = p.post_id 
group by 
     title 
,  content 
,  user_id 

Answer 2

select p.post_id, 
     max(p.title) title, 
     count(case pr.rating when 1 then 1 else null end) lovecount, 
     count(case pr.rating when 2 then 1 else null end) hatecount 
from YourPostsTable p 
left join post_rating pr on p.post_id = pr.post_id 
group by p.post_id