A better question is, how many students are there?
select count ( * ) from person where job = "student"
Yes
select count ( * ) from person where job ! = "student"
What are their names?
select name from person where job ! = "student"
And the names of the people who are not students?
select name from person where job ! = "student"
I need to know how many people there are whose age is greater than 30 and job is an engineer.
select count ( * ) from person where age > 30 and job = 'engineer'