表中每行的另一个表中的项数

Question

当我有这个查询时，我有一个用户配置文件列表。 我想为每个（每个）用户检索nr个关注者，但我只从查询中获得一行结果（有很多用户）

$this->db->select('up.name, up.id, up.image, up.name_id, up.created, COUNT(followers.user_id) as followed_by_count');
$this->db->join('user_profiles up', 'u.id = up.user_id', 'left');
$this->db->join('followers', 'up.user_id = followers.user_id', 'left');

//Something like this? (It doesn't work)
//$this->db->group_by('COUNT(followers.user_id) as followed_by_count'); 
//When tried this I get:
//"You have an error in your SQL syntax; check the manual that corresponds to your  
//MySQL server version for the right syntax to use near 'as followed_by_count"

$this->db->order_by('up.created', 'DESC');

我想我应该以某种方式使用group by？不使用followers-table时查询有效。它也适用于不使用group_by但我显然没有得到我想要的计数。

Answer 1

更改

$this->db->group_by('COUNT(followers.user_id) as followed_by_count'); 

要

$this->db->group_by('u.id'); 

注意：此代码根据您给定的代码给出，并假设您的代码在语法上是正确的。