Foreign Key | PostgreSQL Tutorial

Foreign Key in Database Constraints helps you write SQL that is easier to test, review, and operate at scale.

Introduction to Foreign Key

Use Foreign Key to enforce integrity rules directly in the database.

Commonly paired with: SELECT, FROM, WHERE, WITH.

Practical examples with Foreign Key in PostgreSQL

Reference pattern: start from canonical syntax and keep it explicit.

CREATE TABLE orders (
  order_id BIGSERIAL PRIMARY KEY,
  customer_id BIGINT REFERENCES customers(customer_id)
);

Production-style scenario: apply the same concept to realistic application data.

BEGIN;
ALTER TABLE orders ADD COLUMN IF NOT EXISTS updated_at TIMESTAMPTZ DEFAULT now();
CREATE INDEX IF NOT EXISTS idx_orders_updated_at ON orders (updated_at DESC);
COMMIT;

Additional example: use a variation to validate behavior and edge cases.

ALTER TABLE orders
ADD CONSTRAINT orders_total_nonnegative CHECK (total_amount >= 0);

Production tips

Prefer explicit column lists and deterministic ordering when results feed APIs or batch jobs.
Validate plans with EXPLAIN before adding indexes, then re-check after schema changes.
Keep DDL, data backfills, and cleanups in transactions when possible to avoid partial state.
Use isolated environments for risky changes so query tuning and schema experiments stay safe.

Vela workflow tip

Test this pattern in an isolated branch database, share the result with your team, and promote only after query plans and row counts look correct.

Reference: PostgreSQL official documentation.