如何使用 codeigniter 查询获得每个产品的平均评分？

Question

我有评分 table，其中有用户给出的每个产品的评分，我正在检索所有评分记录，但同时我想获得基于每个产品的平均评分，但我无法得到输出

查询：

$this->db->select('ratings.*');
$this->db->select('select AVG(ratings) as avg_rating from ratings group by product_id');
$this->db->from('ratings');
$this->db->join('users','users.id=ratings.user_id');
$this->db->get()->result();

评分table

id   user_id product_id  rating  

1      4         1         4
 
2      5         2         4

3      6         1         2


4      7         4         4

预期输出：

id   user_id product_id  rating          avg rating

1      4         1         4               3
 
2      5         2         4               4

3      6         1         2               3


4      7         4         4               4

Answer 1

当查询变得复杂时，我喜欢使用查询而不是查询生成器。你可以这样做：

$this->db->query('select r.*,(select round(sum(r2.rating)/count(*),0) from ratings r2 where r2.product_id = r.product_id ) as 'avg rating' from ratings r')->result();

Answer 2

从 table ratings 获取数据，对平均值使用左连接 select。

Codeigniter 的 join() function 允许你写 select 部分而不是 table 名称，但你需要将其放在括号中：

$this->db->select('t1.*, t2.avg_rating, t3.*');
$this->db->from('ratings t1');
$this->db->join('
                  (select product_id, avg(rating) as avg_rating 
                   from ratings 
                   group by product_id)  t2','t2.product_id=t1.product_id','left'
                );
$this->db->join('users t3','t3.id=t1.user_id','left'); 
$this->group_by('t1.userid')
$this->db->get()->result();

生成：

SELECT t1.*, t2.avg_rating, t3.*
FROM ratings t1
left join 
        (select product_id, avg(rating) as avg_rating from ratings group by product_id)  t2 
    on t2.product_id=t1.product_id
left join users t3
    on t1.user_id = t3.id
group by t1.user_id

并按照您的预期输出。

如何使用 codeigniter 查询获得每个产品的平均评分？

How to get avg rating per product using codeigniter query?

php

mysql

codeigniter

average