DDL

PostgreSQL NOT VALID Constraints Separate Enforcement from Table Scans

Adding a constraint to a populated PostgreSQL table can combine two distinct jobs: establish enforcement for future writes and prove that every existing row already satisfies the rule. NOT VALID separates those jobs for foreign-key and check constraints. The constraint becomes active for later inserts and updates, while verification of older rows is deferred. That separation changes the locking profile of a schema migration without changing the intended final constraint. It also creates a temporary catalog state in which PostgreSQL enforces the rule but has not yet established that all stored rows satisfy it.