What are the total number of students in each department?
select count ( distinct t2.id ), t3.dept_name from department as t1 join student as t2 on t1.dept_name = t2.dept_name join instructor as t3 on t1.dept_name = t3.dept_name group by t3.dept_name
And, do you also have information on the total number of instructors in each department?
select count ( distinct t2.id ), count ( distinct t3.id ), t3.dept_name from department as t1 join student as t2 on t1.dept_name = t2.dept_name join instructor as t3 on t1.dept_name = t3.dept_name group by t3.dept_name
Total number of students.
select count ( * ) from student
Do you know the name of the Astronomy instructor?
select t2.name from department as t1 join instructor as t2 on t1.dept_name = t2.dept_name where t1.dept_name = 'Astronomy'
Lastly, do you have his salary?
select t2.name,t2.salary from department as t1 join instructor as t2 on t1.dept_name = t2.dept_name where t1.dept_name = 'Astronomy'