ClassesMoreThan5Students.sql

-- Table: Courses

-- +-------------+---------+
-- | Column Name | Type    |
-- +-------------+---------+
-- | student     | varchar |
-- | class       | varchar |
-- +-------------+---------+
-- (student, class) is the primary key (combination of columns with unique values) for this table.
-- Each row of this table indicates the name of a student and the class in which they are enrolled.
 
-- Write a solution to find all the classes that have at least five students.

-- Return the result table in any order.

-- The result format is in the following example.

-- Example 1:

-- Input: 
-- Courses table:
-- +---------+----------+
-- | student | class    |
-- +---------+----------+
-- | A       | Math     |
-- | B       | English  |
-- | C       | Math     |
-- | D       | Biology  |
-- | E       | Math     |
-- | F       | Computer |
-- | G       | Math     |
-- | H       | Math     |
-- | I       | Math     |
-- +---------+----------+
-- Output: 
-- +---------+
-- | class   |
-- +---------+
-- | Math    |
-- +---------+
-- Explanation: 
-- - Math has 6 students, so we include it.
-- - English has 1 student, so we do not include it.
-- - Biology has 1 student, so we do not include it.
-- - Computer has 1 student, so we do not include it.


-- Write your PostgreSQL query statement below
-- Solution

select C.class 
from (
    select class,
        count(student) as student_count
    from Courses group by class
) C where C.student_count >= 5