Check constraints ensure that the value in a constrained column always satisfies the boolean expression that was specified when the check constraint was defined.
- CURRENT VALIDTIME CHECK constraints are enforced only on rows that are current and future in valid time. Consequently, modifications to rows that are history rows in valid time are not checked for constraint violations.
- SEQUENCED VALIDTIME CHECK constraints are enforced on history, current, and future rows in valid time.
- NONSEQUENCED VALIDTIME CHECK constraints treat the valid-time column as a nontemporal column, so act like a check constraint on a nontemporal table, and are enforced on all open rows of the table. This means nonsequenced and sequenced check constraints have identical effects on temporal tables.