refactor 596

Author: fishercoder1534

database/_596.sql

@@ -1,3 +1,36 @@
+--596. Classes More Than 5 Students
+--SQL Schema
+--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;