PostgreSQL is a database server that stores related facts in tables and lets clients query them with SQL. Schemas organize names; primary and foreign keys identify and connect rows; constraints reject invalid state; transactions make groups of changes atomic; and indexes accelerate chosen access paths. pgvector extends this foundation rather than replacing it.
Think of PostgreSQL as a carefully controlled shared notebook:
The server—not the client—enforces data types, constraints, permissions, and transaction rules.
The primary key identifies a row. The foreign key prevents orphan chunks. NOT NULL, CHECK, and UNIQUE reject invalid states. ON DELETE CASCADE deliberately propagates document deletion to its chunks; use it only when that lifecycle is correct.
A transaction makes a set of statements succeed or fail as one unit:
If an error occurs before COMMIT, use ROLLBACK. Atomicity is valuable when a document state and its derived retrieval records must change together.
An index is an access structure that may speed selected queries. A unique index can enforce uniqueness, but ordinary indexes do not validate business meaning. Constraints define valid state; query indexes optimize access. Vector indexes are also access structures: adding one can change which approximate neighbors are returned, not the underlying rows.
In psql, inspect the schema:
Try inserting a chunk with a missing document ID and observe the foreign-key error. Run it inside a disposable learning database. The rejected row is evidence that the server—not your application UI—protects the relationship.
Review this PostgreSQL schema for a multi-tenant document retrieval system: [paste schema]. Identify entities, keys, lifecycle rules, invariants, and ambiguous delete behavior. Propose constraints before proposing indexes. Return migration SQL and five deliberately invalid inserts that should fail.
Verification contract: Run each invalid insert inside BEGIN; ... ROLLBACK; and confirm the expected constraint name appears.