Check out example codes for "codeigniter where order by". It will help you in understanding the concepts better.

Code Example 1

$this->db->select('ae_users.employee_id, ae_users.emp_name, ae_users.emp_name2, ae_users.emp_name3');
		$this->db->from('ae_users');                
		$this->db->where_in('ae_users.employee_id',$employee_ids);
     
		$query =$this->db->get();
             
		if ($query->num_rows()) {
			return $query->result_array();
		} else {
			return 0;
		}

Code Example 2

$this->db->select('ae_users.employee_id, ae_users.emp_name, ae_users.emp_name2, ae_users.emp_name3');
		$this->db->from('ae_users');                
		$this->db->where_in('ae_users.employee_id',$employee_ids);
                $this->db->_protect_identifiers = FALSE; // stop CI adding backticks
                $order = sprintf('FIELD(ae_users.employee_id, %s)', implode(', ', $employee_ids));
                $this->db->order_by($order);
                $this->db->_protect_identifiers = TRUE; 
		$query =$this->db->get();
               // echo '<pre>'; print_r($this->db->last_query());exit;
		if ($query->num_rows()) {
			return $query->result_array();
		} else {
			return 0;
		}

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