After dropping null night readings, a water-meter set has fewer non-null rows than the operations rule requires for a valid day. Which dataset constraint should the tester apply?

After dropping null night readings, the set has fewer non-null rows than the operations rule requires for a valid day. That is a multi-value count constraint on non-null attributes or instances. A sum constraint hunts a points cap, a useful-value constraint hunts an all-unique ticket number, and skipping the day misses the floor.