CREATE TABLE grades (name TEXT, subject TEXT, grade INTEGER);

INSERT INTO grades (name, subject, grade) VALUES
    ("John", "CompSci", 97), ("Eric", "CompSci", 88), ("Carol", "Arts", 99),
    ("John", "History", 93), ("Andrew", "History", 82), ("Eric", "History", 87),
    ("Steve", "Physics", 91), ("John", "Physics", 84), ("Barney", "Physics", 97);

SELECT "all names", COUNT(name) FROM grades;
SELECT "unique names", COUNT(DISTINCT name) FROM grades;
SELECT DISTINCT name FROM grades;