Iterative LIFO accounting, Sql Server

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create table #T
(
    stockId int not null,
    dealId int identity (1,1) not null,
    dealType char(1) not null,
    stockDate datetime not null,
    stockAmount int not null,
    pricePerStock int not null
);

insert into #T (stockId, dealType, stockDate, stockAmount, pricePerStock) values
    (111, 'B', '01.03.2016', 10, 5),
    (111, 'B', '02.03.2016', 15, 6),
    (111, 'B', '03.03.2016',  5, 4),
    (111, 'S', '04.03.2016', 17, 7),
    (111, 'B', '05.03.2016',  3, 8),
    (111, 'S', '06.03.2016',  4, 8),
    (111, 'S', '07.03.2016',  8, 9);

select * from #T;

create table #R
(
    lvl int not null,
    stockId int not null,
    dealId int not null,
    stockDate datetime not null,
    stockAmount int not null,
    pricePerStock int not null,
    stockRemaining int not null,
    amountDeducted int not null
);

insert into #R (lvl, stockId, dealId, stockDate, stockAmount, pricePerStock, stockRemaining, amountDeducted)
select 0, stockId, dealId, stockDate, stockAmount, pricePerStock, stockAmount as stockRemaining, 0 as amountDeducted
from #T
where dealtype = 'B'

select * from #R;

declare @rowCount int = 1;
declare @lvl int = 0;

while @rowCount > 0
begin
    set @lvl = @lvl + 1;

with sells as (
        select stockId, dealId as saleId, row_number() over (order by dealId) as sellNum, stockAmount as sellAmount
        from #T where dealType = 'S'
    )
    update #R
    set lvl = @lvl, /* debugging only */
        amountDeducted = (select sellAmount from sells where sellNum = @lvl), /* debugging only */
        stockRemaining = (
            select stockRemaining
            from (
                select dealId,
                    case
                        when r.stockRemaining + s.sellAmount < sum(stockRemaining) over (order by dealId desc) then r.stockRemaining
                        when sum(stockRemaining) over (order by dealId desc) < s.sellAmount then 0
                        else sum(stockRemaining) over (order by dealId desc) - s.sellAmount
                    end as stockremaining
                from sells s inner join #R r on r.stockId = s.stockId and r.dealId < s.saleId
                where s.stockId = #R.stockId and s.sellNum = @lvl
            ) data
            where dealId = #R.dealId
        )
    where dealId < (select saleId from sells where sellNum = @lvl);

set @rowCount = @@rowCount;
    if @rowCount > 0 select * from #R;
end

View schema
Execution time: 0,06 sec, rows selected: 33, rows affected: 22, absolute service time: 0,22 sec