Learn SQL: DISTINCT

Removing duplicates with DISTINCT

"The mayor wants to know which towns our visitors come from," says Noor. "But my list names Hasselt six times." Once is enough.

DISTINCT keeps each row once

Put DISTINCT right after SELECT and each row appears only once in the result, however often it is in the table.

Below you see the same column without DISTINCT: eighteen tickets, with plenty of duplicates.

SELECT DISTINCT town FROM tickets

SELECT town FROM tickets

With several columns, DISTINCT looks at the combination. A day ticket for Friday and a day ticket for Saturday are two different rows.

Here NULL counts as one value: none of the combi tickets has a day, so they appear only once in the result.

SELECT DISTINCT kind, day FROM tickets

For which days were day tickets sold? Show each day once, the earliest first.

The full lesson has 6 exercises, from easy to challenging, with hints, points and a streak you can build.