如何编写此子查询在Codeigniter中选择带限制的AVG

Posted 2021-04-09

SELECT AVG(harian) a from (select harian from sla limit 2) b

以上是在Heidisql中执行的，

并尝试下面：

$rata2 = $this->db->query('SELECT AVG(harian) a from (select harian from sla limit 2) b');

但是，似乎没有输出，请帮助，谢谢

答案

// Sub Query
$this->db->select('harian')->from('sla')->limit(2);
$subQuery =  $this->db->get_compiled_select();

// Main Query
$rata2 = $this->db->select('AVG(harian)')
     ->from($subQuery)
     ->get();

return $rata2; 

或者，如果要返回数组中的数据

// Sub Query
$this->db->select('harian')->from('sla')->limit(2);
$subQuery =  $this->db->get_compiled_select();

// Main Query
$rata2 = $this->db->select('AVG(harian)')
     ->from($subQuery)
     ->get()
     ->toArray();

return $rata2;