sql-not-in-nullable-trap

Why x NOT IN (subquery) matches zero rows and still reports success whenever a NULL is actually present in the subquery result — a standing risk for any nullable column — how to guard every such subquery, and how to make a silently-inert statement detectable instead of invisible. Reach for it when a DELETE or SELECT with a NOT IN filter returns nothing on data you can see with your own eyes, when a cleanup pass…