ALTER TABLE deliveries ADD COLUMN IF NOT EXISTS delivery_slot VARCHAR(20) NULL AFTER scheduled_date;
ALTER TABLE deliveries ADD COLUMN IF NOT EXISTS specific_time CHAR(5) NULL AFTER delivery_slot;
ALTER TABLE deliveries ADD COLUMN IF NOT EXISTS delivery_window_start CHAR(5) NULL AFTER specific_time;
ALTER TABLE deliveries ADD COLUMN IF NOT EXISTS delivery_window_end CHAR(5) NULL AFTER delivery_window_start;