Use the DISTINCT operator to pull unique values from a database, which comes directly after SELECT. For example, if you wanted to see unique values of country from the Users dataset:
SELECT DISTINCT country
FROM getting_started.users
;
To pull unique rows for multiple fields:
SELECT DISTINCT
country
, acquisition_source
FROM getting_started.users
;
And to pull unique rows for an entire dataset:
SELECT DISTINCT * FROM getting_started.payments ;