Try this:
select A.DEPTNAME,
sum(case when B.EMPLOYEE_CLASS='Full time' then B.STAFF_NO else 0) as FullTimeNo,
sum(case when B.EMPLOYEE_CLASS='Part time' then B.STAFF_NO else 0) as PartTimeNo,
from TabA A
join TabB B on A.DEPTNAME=B.DEPTNAME
group by A.DEPTNAME