CodeIgniter：计算连接表的结果 [英] CodeIgniter: Counting results from a joined table

问题描述

现在我知道如何连接两个表格，我想实际计算第二个表格中的活动记录数。

Now I know how to join two tables, I'd like to actually count the number of rows in the second table with active records.

说，我有这两个表：

blog     comments
-------  ----------
id       id
title    blog_id
content  comment

否我想获取最后三个博客条目，并计算每个博客条目的评论数，所有在一个查询。我试过这样，但它不工作：

No I want to take the three last blog entries and count the number of comments per blog entry, all in one query. I tried something like this, but it doesn't work:

$this->db->select('*')
         ->from('blog')
         ->order_by('blog.id', 'desc')
         ->limit(3);

$this->db->join('comments', 'blog_entry_id = blog.id')
         ->group_by('blog_entry_id')
         ->count_all_results('comments'); 

我该怎么办？我做错了什么？

推荐答案

：）

$this->db->select('blog.*, COUNT(comments.id) as num_comments')
         ->from('blog')
         ->order_by('blog.id', 'desc')
         ->limit(3);

$this->db->join('comments', 'blog_entry_id = blog.id')
         ->group_by('blog_entry_id');

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