Keys and relational integrity constraints
Research context
postgraduate concept · established · As of 2026-10-10
A candidate key is a minimal attribute set uniquely identifying a tuple; a superkey need not be minimal.
Key knowledge
A candidate key is a minimal attribute set uniquely identifying a tuple; a superkey need not be minimal. A chosen primary key and declared foreign keys enforce different constraints. A foreign key references a declared unique key and must specify deletion/update behavior and NULL policy. Observing uniqueness in a sample does not establish a schema invariant for future data.
Conditions and scope
- Constraints are properties of permitted database states, not just observed data.
- Composite key uniqueness refers to the tuple of key values; nullable uniqueness has implementation-specific details.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: Keys, superkeys, foreign keys and integrity constraints; §13.2: read committed, repeatable read and serializable; anomalies, serialization failures and retries. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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