Vol. I · A Postgres HandbookTwelve chapters · · 756 queries

The Query & the Schema

A reading-room reference for writing PostgreSQL by hand — selects to window functions, with the schema in plain view.

IntermediateBasic SELECT

Add a UNIQUE constraint

SQL

ALTER TABLE employees 
ADD CONSTRAINT unique_email UNIQUE (email);

Tested against PostgreSQL 16

Note

“Ensures all values in the email column are distinct. Automatically creates a unique B-tree index.