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 employees in each department (just count)

SQL

SELECT
  dept_id,
  COUNT(*) AS employee_count
FROM employees
GROUP BY dept_id;

Tested against PostgreSQL 16

Note

“GROUP BY aggregates rows sharing the same value into summary rows.