Surrogate Keys vs Natural Keys

Surrogate Keys vs Natural Keys#

A startup used email as the primary key in their users table. Clean, readable, self-documenting. Every orders row carried that email as a foreign key. Every sessions row. Every audit log entry. When they added a feature letting users change their email address, they discovered what "cascading update" really means at scale: millions of foreign key references across a dozen tables, a migration that took three days, and t...