如何使用codeigniter和sql获取日期？与数据表

THIS IS MY MODEL:

这是我的模特：

public function GetAttendance($from, $to)
{

    $sql = "SELECT a.empnum,CONCAT(a.name,' ',a.midname,' ',a.lastname) AS
            NAME,CONCAT(b.indate,' ',b.intime) AS 'TIMEIN',CONCAT(b.outdate,'
            ',b.outtime)AS 'TIMEOUT', DATEDIFF('timeout','timein') AS 'DUR' 
            FROM employees AS a
            JOIN times AS b ON (a.empnum=b.userid)
            WHERE b.indate BETWEEN
            STR_TO_DATE('".$from."','%m/%d/%y') AND STR_TO_DATE('".$to."','%m/%d/%y')";

    $query = $this->db->query($sql);

    return $query->result();
}

}
public function G