596-classes_more_than_5_students.sql

-- 596. Classes More Than 5 Students

-- There is a table courses with columns: student and class
-- Please list out all classes which have more than or equal to 5 students.

-- For example, the table:

-- +---------+------------+
-- | student | class      |
-- +---------+------------+
-- | A       | Math       |
-- | B       | English    |
-- | C       | Math       |
-- | D       | Biology    |
-- | E       | Math       |
-- | F       | Computer   |
-- | G       | Math       |
-- | H       | Math       |
-- | I       | Math       |
-- +---------+------------+

-- Should output:

-- +---------+
-- | class   |
-- +---------+
-- | Math    |
-- +---------+

-- Note:
-- The students should not be counted duplicate in each course.

SELECT class 
FROM courses
GROUP BY class
HAVING COUNT(DISTINCT(student)) >= 5;