How do I list the distinct customer values in SQL?

SELECT DISTINCT customer FROM data;

`SELECT DISTINCT customer` returns each unique value that customer takes exactly once, dropping repeats — useful for a quick inventory of what values actually occur in a column before deciding how to filter or group on it.

A table named data with columns: order_id (integer), customer (text), country (text), category (text), quantity (integer), unit_price (real), order_date (text, YYYY-MM-DD).