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Editorial Team
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Asked: 2026-06-14T19:40:04+00:00

This is kind of a followup to my question Reference a column and update

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This is kind of a followup to my question Reference a column and update it in the same statement. I am now trying to use a local variable and have it updated in the same update statement.

declare @tmp table (ID int primary key, UNPAID money)

insert into @tmp select 1, 31.63
insert into @tmp select 2, 49.20
insert into @tmp select 3, 99.00
insert into @tmp select 4, 41.00

declare @paymentAmmount money
select @paymentAmmount = SUM(UNPAID) from @tmp
            
declare cur_oustandingAR cursor local static for select ID  from @tmp order by ID
open cur_oustandingAR

declare @currentID int

fetch next from cur_oustandingAR into @currentID
while (@@fetch_status = 0 and @paymentAmmount > 0)
begin
    begin
        update @tmp
            set UNPAID = case when @paymentAmmount > UNPAID then 0 else UNPAID - @paymentAmmount end,
                @paymentAmmount = case when @paymentAmmount > UNPAID then @paymentAmmount - UNPAID else 0 end
            where ID = @currentID
    end
    fetch next from cur_oustandingAR into @currentID
end

select * from @tmp
select @paymentAmmount as LeftoverPayment

You can run the query here, here is the results it gives

ID          UNPAID
----------- ---------------------
1           0.00
2           0.00
3           58.00
4           41.00

LeftoverPayment 
--------------- 
0

All of the value should of been 0 and @paymentAmmount at the end should also be 0. What is going wrong that is causing the values to not be applied correctly?

P.S. I know how to fix it, just break the one query in to the 3 following queries, but I wanted to do it as a single query so I did not need as many lookups against the real table

select @oldUnpaid = UNPAID from @tmp where ID = @currentID
update @tmp 
    set UNPAID = case when @paymentAmmount > UNPAID then 0 else UNPAID - @paymentAmmount end
    where ID = @currentID
select @paymentAmmount = case when @paymentAmmount > @oldUnpaid then @paymentAmmount - @oldUnpaid else 0 end

I just wanted to know why what I am doing currently does not work.

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1 Answer

  1. Editorial Team
    declare @tmp table (ID int primary key, UNPAID money)

insert into @tmp select 1, 31.63
insert into @tmp select 2, 49.20
insert into @tmp select 3, 99.00
insert into @tmp select 4, 41.00

declare @paymentAmmount money
declare @paymentAmmountbuf money
select @paymentAmmount = SUM(UNPAID) from @tmp
declare cur_oustandingAR cursor local static for select ID  from @tmp order by ID
open cur_oustandingAR

declare @currentID int

fetch next from cur_oustandingAR into @currentID
while (@@fetch_status = 0 and @paymentAmmount > 0)
begin
    begin
        select @paymentAmmountbuf=@paymentAmmount

        update @tmp
            set UNPAID = case when @paymentAmmountbuf > UNPAID then 0 else UNPAID - @paymentAmmountbuf end,
                @paymentAmmount = case when @paymentAmmount > UNPAID then @paymentAmmount - UNPAID else 0 end
            where ID = @currentID
    end
    fetch next from cur_oustandingAR into @currentID
end

select * from @tmp
select @paymentAmmount as LeftoverPayment
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