Below is a basic example for Group By

CREATE TABLE #Studentcourseschedule(

Department int,

Courseid int,

studentid int)

go

insert into #Studentcourseschedule(Department, Courseid,studentid)

values(1,1,1)

,(1,2,1)

,(1,3,1)

,(1,1,5)

,(1,3,6)

,(1,1,7)

,(2,2,1)

,(2,1,2)

,(2,3,2)

go

select department, COUNT(studentid) Studentcount

from #Studentcourseschedule

group by department

order by Department

go

select department, courseid, COUNT(studentid) Studentcount

from #Studentcourseschedule

group by department,courseid

order by Department, Courseid

1st Query Result:

department Studentcount

1 6

2 3

2nd Query Result

departmentcourseidStudentcount

1 1 3

1 2 1

1 3 2

2 1 1

2 2 1

2 3 1

In the first query the grouping is done only on Department, so it checks the no of students in each of the Department available in the table which is 1 and 2 in example

When we add another group by column on courseid, now it looks for the each course available under each department and displays count of the student in that department and course.