Databases · Flashcard
What does WITHOUT OVERLAPS do in a PostgreSQL 18 PRIMARY KEY declaration?
- AThe last column is compared for overlap rather than equality, so a key may repeat over disjoint periods
- BThe last column is dropped from the key itself and carried in the index only as a payload for scans
- CThe key stops enforcing uniqueness altogether and rejects a row only when two periods are identical
- DThe key forces an ordering on that column so the index accepts periods in ascending sequence only
Why this is the answer
PRIMARY KEY (id, valid_period WITHOUT OVERLAPS) is a temporal key: the same id may appear many times as long as no two of its periods overlap, which is exactly the rule a history of states needs. The period column is a full part of the key rather than a payload, uniqueness is strengthened rather than dropped, and nothing about insert ordering is constrained.
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