php - Codeigniter 2.1 - 连接两个表并在同一个查询中计数

Question

我有两张桌子：

news ->     
  id_news    
  title    
  body    
  date_created    
  image    
  category_id    

comments ->     
  id_comments    
  news_id    
  body    
  date_created

如何编写查询以获取所有新闻，计算每条新闻的所有评论并在视图部分显示该查询？

Answer 1

select
      N.ID_News,
      N.Title,
      N.Body,
      N.Date_Created,
      N.Image,
      N.Category_ID,
      count(C.ID_Comments) CommentCount
   from
      News N
         LEFT JOIN Comments C
            on N.ID_News = C.News_ID
   group by 
      N.ID_News
   order by
      whatever column(s) are important to you

Answer 2

由于我们正在计数，我们需要对 DRap 的 Query 做一个小改动：

select
      N.ID_News,
      N.Title,
      N.Body,
      N.Date_Created,
      N.Image,
      N.Category_ID,
      count(C.ID_Comments) CommentCount
   from
      News N
         LEFT JOIN Comments C
            on N.ID_News = C.News_ID
   order by
      whatever column(s) are important to you

那只会给你一个结果..由于该查询缺少 group by 语句，我建议将该查询更改为：

select
      N.ID_News,
      N.Title,
      N.Body,
      N.Date_Created,
      N.Image,
      N.Category_ID,
      count(C.ID_Comments) CommentCount
   from
      News N
         LEFT JOIN Comments C
            on N.ID_News = C.News_ID
   group by
      N.title
   order by
      whatever column(s) are important to you

Answer 3

以 Active Record 格式写下来是这样的：

$this->db->select('N.ID_News, N.Title, N.Body, N.Date_Created, N.Image')
$this->db->select('N.Category_ID, count(C.ID_Comments) AS CommentCount');
$this->db->from('News AS N');
$this->db->join('commentas AS C', 'N.ID_News = C.News_ID', 'left');
$this->db->group_by('N.title');

在此之后，您可以使用按功能排序，根据需要对结果进行排序。