Question

I have a table that I want to find for each row id the amount remaining from the total. However, the order of amounts is in an ascending order.

id   amount
1    3
2    2
3    1
4    5

The results should look like this:

id   remainder
1    10
2    8
3    5
4    0

Any thoughts on how to accomplish this? I’m guessing that the over clause is the way to go, but I can’t quite piece it together.Thanks.

Answer 1

SQL Server 2008 answer, I can’t provide an SQL Fiddle, it seems it strips the begin keyword, resulting to syntax errors. I tested this on my machine though:

create function RunningTotalGuarded()
returns @ReturnTable table(
    Id int, 
    Amount int not null, 
    RunningTotal int not null, 
    RN int identity(1,1) not null primary key clustered
)

as
begin

  insert into @ReturnTable(id, amount, RunningTotal) 
  select id, amount, 0 from tbl order by amount;

  declare @RunningTotal numeric(16,4) = 0;
  declare @rn_check int = 0;

  update @ReturnTable
    set 
        @rn_check = @rn_check + 1
        ,@RunningTotal = 
        case when rn = @rn_check then
            @RunningTotal + Amount
        else
            1 / 0
        end
        ,RunningTotal = @RunningTotal;     
  return;    
end;

To achieve your desired output:

with a as
(
    select *, sum(amount) over() - RunningTotal as remainder
        , row_number() over(order by id) as id_order
    from RunningTotalGuarded()
)
select a.id, amount_order.remainder
from a
inner join a amount_order on amount_order.rn = a.id_order;

Rationale for guarded running total: http://www.ienablemuch.com/2012/05/recursive-cte-is-evil-and-cursor-is.html

Choose the lesser evil 😉