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.

EasyBasic SELECT

Count distinct departments in employees table

SQL

SELECT COUNT(DISTINCT dept_id) AS unique_departments
FROM employees;

Tested against PostgreSQL 16

Note

“COUNT(DISTINCT col) counts unique non-null values. Different from COUNT(*) which counts all rows.