MySQL: DISTINCT reference

In a nutshell

The DISTINCT keyword is used in conjunction with the SELECT statement to eliminate duplicate rows from a result set.

What is regarded as a duplicate row depends on the columns you pass to DISTINCT.

DISTINCT without any columns

SELECT DISTINCT * FROM students;

Two rows are duplicates if every column in both rows are the same.

DISTINCT with a single column

SELECT DISTINCT first_name FROM students;

Two rows are duplicates if the first_name column of both rows is the same.

DISTINCT with multiple columns

SELECT DISTINCT first_name, last_name FROM students;

Two rows are duplicates if the first_name and last_name columns of both rows is the same.