ClassesMoreThan5Students.sql

# Source : https://leetcode.com/problems/classes-more-than-5-students
# Author : Dean Shi
# Date   : 2017-08-16

##################################################################################
#
#  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