SQL | Aggregation - sql

Question

My objective is to get a table such as this:
Request:
Wards where the annual cost of drugs prescribed exceeds 25
ward_no | year | cost
w2 | 2007 | 34
w4 | 2007 | 160
w5 | 2006 | 26
w5 | 2007 | 33
I would input a picture but lack reputation points.
Here is what I have done so far:
select w.ward_no,
year(pn.start_date) as year,
pn.quantity * d.price as cost
from ward w,
patient pt,
prescription pn,
drug d
where w.ward_no = pt.ward_no
and
pn.drug_code = d.drug_code
and
pn.patient_id = pt.patient_id
group by w.ward_no,
year,
cost
having cost > 25
order by w.ward_no, year
My current output is such:
ward_no|year|cost
'w2' |2006|0.28
'w2' |2007|3.20
'w2' |2007|9.50
'w2' |2007|21.60
'w3' |2006|10.08
'w3' |2007|4.80
'w4' |2006|4.41
'w4' |2007|101.00
'w4' |2007|58.80
'w5' |2006|25.20
'w5' |2006|0.56
'w5' |2007|20.16
'w5' |2007|12.60
How would I reduce each ward_no to have only a single row of year (say 2006 or 2007) instead of having x of them?
Any help would be very much appreciated I am really stuck and have no clue what to do.

Answer 1

You need to group by ward and year, and sum up the costs:
select w.ward_no,
year(pn.start_date) as year,
sum(pn.quantity * d.price) as cost
from ward w
inner join patient pt
on pt.ward_no = w.ward_no
inner join prescription pn
on pn.patient_id = pt.patient_id
inner join drug d
on d.drug_code = pn.drug_code
group by w.ward_no,
year(pn.start_date)
having sum(pn.quantity * d.price) > 25
order by w.ward_no, year
What flavor of SQL is this supposed to be for?
Share and enjoy.

Answer 2

You are grouping by cost, so each cost gets a new line. Remove the cost from your grouping
select w.ward_no,
year(pn.start_date) as year,
avg(pn.quantity * d.price) as cost
from ward w,
patient pt,
prescription pn,
drug d
where w.ward_no = pt.ward_no
and
pn.drug_code = d.drug_code
and
pn.patient_id = pt.patient_id
group by w.ward_no,
year
having avg(pn.quantity * d.price) > 25
order by w.ward_no, year