I really new to SQL, currently learning PostgreSQL.
Suppose I have the following schema:
class(class_id, school_name), primary key: (class_id)
enroll(student_id, class_id), primary key: (student_id, class_id)
I want to find the class_id where the class’ sum of enrolled student is at least 10% higher than average.
I know that I can find sum of enrollment for any class by
SELECT E.class_id, COUNT(*) FROM enroll E GROUP BY E.class_id
But how do I compare one to the other in percentage?
here’s your query, you can use
select t1.class_id, t1.ct from (select count(1)ct, class_id from enroll group by class_id) t1 group by t1.class_id having avg(t1.ct) > (t1.ct * .10)