Question

when i join two tables together and get the sum, i am getting the correct figure:

select 
    d.accn_id,
    cast(d.load_date as DATE) as LoadDate,
    cast (d.final_rpt_date as DATE) as FinalReportDate,
    sum(p.paid_amt) as SumPaidAmt

from
    accn_demographics d
join 
    accn_payments p
on 
    d.ACCN_ID=p.ACCN_ID
where 
    p.POSTED='y'
    and p.PMT_DATE between '20120501' and '20120531'

group by 
    d.accn_id,
    d.load_date,
    d.final_rpt_date

however after i join ANOTHER table accn_payors:

select 
    d.accn_id,
    cast(d.load_date as DATE) as LoadDate,
    cast (d.final_rpt_date as DATE) as FinalReportDate,
    sum(p.paid_amt) as SumPaidAmt
    ,payors.PAYOR_ID
from
    accn_demographics d
join 
    accn_payments p
on 
    d.ACCN_ID=p.ACCN_ID
left join 
    accn_payors payors
on  
    payors.X_PAYOR_ID=p.X_PRICED_PAYOR_ID 
    and payors.ACCN_ID = p.ACCN_ID
where 
    p.POSTED='y'
    and p.PMT_DATE between '20120501' and '20120531'

group by 
    d.accn_id,
    d.load_date,
    d.final_rpt_date
    ,payors.PAYOR_ID

i am getting an overstatement of sum(p.paid_amt)

the question is how can i adjust my join so that i am not joining multiple times?

Answer 1

Instead of joining on accn_payors, you need to join on a SELECT statement that returns one row per accn_id. Depending on your requirements, this might work.

select accn_id, min(x_payor_id) x_payor_id
from payors
group by accn_id

Aliasing min(x_payor_id) with the same name lets the rest of the code work without modification. That might or might not be a good idea. It’s a little misleading.

So instead of this . . .

left join 
    accn_payors payors
on  
    payors.X_PAYOR_ID=p.X_PRICED_PAYOR_ID 
    and payors.ACCN_ID = p.ACCN_ID

you’d do this . . .

left join 
    (select accn_id, min(x_payor_id)
     from payors
     group by accn_id) payors
on  
    payors.x_payor_id = p.x_priced_payor_id
    and payors.accn_id = p.accn_id