databaselisted

# Database Use this skill for persistence, queries, schema changes, migrations, transactions, data integrity, and data-access behavior. This skill is language, ORM, and database framework agnostic. ## Data Integrity Enforce important invariants at the strongest practical layer. Use appropriate: - constraints - uniqueness rules - foreign keys - nullability - validation - transaction boundaries Application validation does not replace database integrity where concurrent writes can violate an invariant. ## Queries Prefer structured and parameterized query mechanisms. Avoid: - unbounded reads - unnecessary columns - repeated identical queries - N+1 access patterns - avoidable full scans - query construction from untrusted input Inspect the actual workload before adding optimization complexity. ## Transactions Use transactions when multiple operations must succeed or fail as one logical change. Keep transaction scopes as small as practical. Consider: - partial failure - retries - deadlocks - external side effects - long-running work Do not hold database transactions open while performing unnecessary external operations. ## Concurrency When correctness depends on concurrent access, explicitly consider: - lost updates - duplicate creation - stale reads - locking - atomic operations - optimistic concurrency - idempotency Do not assume application-level checks remain valid between read and write. ## Schema Changes Schema changes should consider: - backwards com