如何将其转换为codeigniter查询样式

 SELECT `users`.`first_name`, `user_profile`.`user_id`, 
`user_profile`.`image`, `messages`.* FROM `messages` LEFT JOIN `user_profile` ON 
`user_profile`.`user_id` = `messages`.`from_id` LEFT JOIN `users`ON `users`.`id` 
= `messages`.`from_id`  WHERE (messages.delete_from != '9' AND messages.delete_to 
!='9’)  AND ( `messages`.`members` = '4,9' OR `messages`.`members` = '9,4' ) 
ORDER BY `date` ASC

$this->db->from($this->table);
$this->db->select('users.first_name,user_profile.user_id,user_profile.image,messages.*');
$this->db->join('user_profile', 'user_profile.user_id =  messages.from_id','left'); 
$this->db->join('users', 'users.id = messages.from_id','left'); 
$this->db->where($id1);
$this->db->where($id2);
$this->db->group_start();
$this->db->where('messages.members',$con1);
$this->db->or_where('messages.members',$con2);
$this->db->group_end();
$this->db->order_by('date','asc');

使用$this->db->group_start();和$this->db->group_end();作为括号