子查询 where 来自 codeigniter 中不同表的条件

Question

通过使用子查询库函数，如何从子查询中的两个表中选择符合条件的记录...？

这是实际的sql查询

SELECT *, (SELECT count('report_id') 
           FROM report 
           WHERE report.category = category.cat_id 
                 and report.user_id IN (68, 69, 70)) AS cnt 
FROM (`category`)

我需要 codeigniter 中的等价物：

    $this->db->select('*')->from('category');
    $sub = $this->subquery->start_subquery('select');
    $sub->select("count('report_id')")->from('report')
        ->where_in(array('user_id'=>(68, 69, 70)));
    $this->subquery->end_subquery('number'); 

在这我怎么能把我的第二个条件...？？？

Answer 1

顺便说一句，是否真的需要依赖子查询，这只会增加负载，它将对类别表中的每一行执行，您可以将等效连接查询编写为

SELECT c.*, 
COUNT(DISTINCT r.report_id) AS cnt /*you can omit distinct if you have unique report ids  */
FROM `category` c
LEFT JOIN report r ON r.category = c.cat_id AND r.user_id IN (68, 69, 70)
GROUP BY c.cat_id

和活动记录查询一样

$result = $this->db->select('c.*,COUNT(DISTINCT r.report_id) AS cnt ',FALSE)
    ->from('category c')
    ->join('report r','r.category = c.cat_id AND r.user_id IN (68, 69, 70)','LEFT')
    ->group_by('c.cat_id')
    ->get()
    ->result();