postgresql 메뉴얼 사이트

https://www.postgresql.org/docs/manuals/

http://yeobi27.tistory.com/entry/PostgreSQL-%EC%A0%9C%EC%95%BD%EC%A1%B0%EA%B1%B4-ConstraintNOT-NULL-UNIQUE-PRIMARY-KEY%EA%B8%B0%EB%B3%B8%ED%82%A4-FOREIGN-KEY%EC%99%B8%EB%9E%98%ED%82%A4