SELECT
                                    event_date,
                                    driver_id,
                                    COUNT(*) AS total_assignments
                                FROM
                                  (
                                    SELECT
                                        DATE(TIMESTAMP_ADD(created_at, INTERVAL 6 HOUR)) as event_date,
                                        tracking_id,
                                        driver_id
                                    FROM order_order2
                                    CROSS JOIN UNNEST(split(order_order2.drivers_tried, ',')) AS driver_id
                                    where
                                        driver_id <> ''
                                        and DATE(TIMESTAMP_ADD(created_at, INTERVAL 6 HOUR)) between '2019-04-01' and '2019-05-15'
                                  )
                                  GROUP BY 1, 2