Query : Find employee count

select ppg.group_name, count(*)
from per_all_people_f ppl, per_all_assignments_f paf, pay_people_groups ppg
where ppl.person_id = paf.person_id
and ppl.current_employee_flag = 'Y'
and paf.assignment_type = 'E'
and paf.people_group_id = ppg.people_group_id (+)
and ppl.effective_start_date <= TO_DATE('31/12/2009','DD/MM/YYYY') and ppl.effective_end_date >= TO_DATE('01/01/2009','DD/MM/YYYY')
and paf.effective_start_date <= TO_DATE('31/12/2009','DD/MM/YYYY') and paf.effective_end_date >= TO_DATE('01/01/2009','DD/MM/YYYY')
group by ppg.group_name