Classes With At Least 5 Students SQL Query

Problem statement

Prompt

Given the courses table below (one row per student enrollment), write a query that returns the class of every class with at least five students.

Output a single column: class.
The order of the result does not matter.
Each row is one enrollment; count rows per class.

Example

student	class
A	Math
B	Math
C	Math
D	Math
E	Math
F	English

Expected result:

class
Math

Constraints

There is no primary key; a student may have duplicate rows for the same class.

Tips

GROUP BY class then HAVING COUNT(*) >= 5.

Schema

CREATE TABLE courses (
    student TEXT NOT NULL,
    class   TEXT NOT NULL
);

Sample data

INSERT INTO courses (student, class) VALUES
  ('A', 'Math'),
  ('B', 'Math'),
  ('C', 'Math'),
  ('D', 'Math'),
  ('E', 'Math'),
  ('F', 'Math'),
  ('A', 'English'),
  ('B', 'English'),
  ('C', 'English'),
  ('D', 'English');

Additional hidden fixtures are applied during validation to test edge cases.

Solution

One correct approach — try solving it yourself in the practice editor first, then compare. There is usually more than one valid solution.

-- Reference: classes with at least five enrollments.
SELECT class
FROM courses
GROUP BY class
HAVING COUNT(*) >= 5
ORDER BY class;

Key concepts

GROUP BY
HAVING
COUNT

Classes With At Least 5 Students