以codeigniter样式编写联合查询

Question

如何以Codeigniter样式编写以下查询.

SELECT COUNT(`id`) AS reccount
  FROM 
    (SELECT `id` FROM table1 
     WHERE tid= '101' AND `status` =  1
     UNION ALL
    SELECT `id` FROM table2 
     WHERE tid= '101' AND `status` =  1
     UNION ALL
    SELECT `id` FROM table3
     WHERE tid= '101' AND `status` =  1) t

我用以下方法执行它.

这是唯一正确的方法还是你有任何改进建议？

 $q = $this->db->query(SELECT COUNT(`id`) AS reccount
                        FROM 
                        (SELECT `id` FROM table1 
                         WHERE tid= '101' AND `status` =  1
                         UNION ALL
                         SELECT `id` FROM table2 
                         WHERE tid= '101' AND `status` =  1
                         UNION ALL
                         SELECT `id` FROM table3
                         WHERE tid= '101' AND `status` =  1) t ");

Answer 1

从CodeIgniter 3开始,它在Active Record中引入了一个函数get_compiled_select(),它给出了查询字符串而没有实际执行查询.

这允许@MDeSilva方法使用更少的资源,调整如下:

function get_merged_result($ids){                   
    $this->db->select("column");
    $this->db->distinct();
    $this->db->from("table_name");
    $this->db->where_in("id",$model_ids);
    $query1 = $this->db->get_compiled_select(); // It resets the query just like a get()

    $this->db->select("column2 as column");
    $this->db->distinct();
    $this->db->from("table_name");
    $this->db->where_in("id",$model_ids);
    $query2 = $this->db->get_compiled_select(); 

    $query = $this->db->query($query1." UNION ".$query2);

    return $query->result();
}