SQL | Aggregation

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 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

Answer 2

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?

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