//get first day of the current month
$start = date("Y-m-1 00:00:00");
//get current date of the month
$end = date("Y-m-d H:i:s");
//query data for the current month so far
$query = $this->db_model->run_query("select column_1, column_2 from table where date_column BETWEEN '".$start."' AND '".$end."'");