The plain-English version
A primary key uniquely identifies a row using one or more non-null columns. A foreign key enforces references to valid keys in the same or another table, subject to the database’s null and update/delete rules.
Why it matters
Database constraints can enforce valid relationships.
The docs behind it
Documentation links checked .
Editorial review · October 28, 2026
Corrected: Makes uniqueness, non-null primary keys, composite keys, and enforced references explicit.