DISTINCT

DISTINCT removes duplicate rows from the result — it looks at the full row (or the listed columns) and collapses repeats down to one.

Source data — Pattern 1: Basic Data Retrieval

All queries run against the shared employees table (see schema.sql).

DISTINCT — source table 1

What it does

DISTINCT removes duplicate rows from the result — it looks at the full row (or the listed columns) and collapses repeats down to one. It runs after the columns are selected, so SELECT DISTINCT department_id only cares about duplicate department_id values, not the whole row.

Problem

Find all unique departments.

SELECT DISTINCT department_id
FROM employees;

DISTINCT — result 1

Tip

To show department names instead of IDs, this pairs naturally with a JOIN to departments — worth cross-linking once Pattern 6 is live.