Question

I’m taking a database course this semester, and we’re learning SQL. I understand most simple queries, but I’m having some difficulty using the count aggregate function.

I’m supposed to relate an advertisement number to a property number to a branch number so that I can tally up the amount of advertisements by branch number and compute their cost. I set up what I think are two appropriate new views, but I’m clueless as to what to write for the select statement. Am I approaching this the correct way? I have a feeling I’m over complicating this bigtime…

with ad_prop(ad_no, property_no, overseen_by) as
  (select a.ad_no, a.property_no, p.overseen_by
   from advertisement as a, property as p
   where a.property_no = p.property_no)
with prop_branch(property_no, overseen_by, allocated_to) as
  (select p.property_no, p.overseen_by, s.allocated_to
   from property as p, staff as s
   where p.overseen_by = s.staff_no)

select distinct pb.allocated_to as branch_no, count( ??? ) * 100 as ad_cost

from prop_branch as pb, ad_prop as ap
where ap.property_no = pb.property_no
group by branch_no;

Any insight would be greatly appreciated!

Answer 1

You could simplify it like this:

advertisement
– ad_no
– property_no

property
– property_no
– overseen_by

staff
– staff_no
– allocated_to

SELECT s.allocated_to AS branch, COUNT(*) as num_ads, COUNT(*)*100 as ad_cost 
FROM advertisement AS a
INNER JOIN property AS p ON a.property_no = p.property_no
INNER JOIN staff AS s ON p.overseen_by = s.staff_no
GROUP BY s.allocated_to;

Update: changed above to match your schema needs