create table dbo.Claims (
  id int not null identity primary key,
  сreated datetime not null,
  item varchar(50) not null,
  quantity float
)

create table dbo.Incomings (
  id int not null identity primary key,
  item varchar(50) not null,
  quantity float
)

create table zcx.IncomingLinks (
  id int identity not null primary key,
  claim_id int not null,
  incoming_id int not null,
  quantity float not null,
  constraint fk_claim_id foreign key (claim_id) references dbo.Claims (id),
  constraint fk_incoming_id foreign key (incoming_id) references dbo.Incomings (id)
)

declare
  cr cursor local for
    with cte as (
      select
        l.id, l.item, l.created, l.quantity,
        l.quantity-isnull(f.purchased, 0) rest,
        row_number() over(partition by l.item order by l.created) priority
      from dbo.claims l
      outer apply (
        select sum(i.quantity)
        from dbo.IncomingLinks i
        where i.claim_id=l.id
      )f(purchased)
    )
    select id, item, rest from cte
    where rest>0
    order by item desc, priority
declare
  @id int,
  @incoming_id int,
  @item varchar(50),
  @rest float,
  @purchased float;
open cr;
while 1=1
begin
  fetch next from cr into @id, @item, @rest;
  if @@fetch_status<>0 break;
  while 1=1
  begin
    set @purchased=null;
    select top 1
      @incoming_id=id,
      @purchased=case when i.quantity - isnull(f.purchased, 0)>@rest then @rest else i.quantity - isnull(f.purchased, 0) end
    from dbo.Incomings i
    outer apply (
      select sum(l.quantity)
      from dbo.IncomingLinks l
      where l.incoming_id=i.id
    )f(purchased)
    where i.item=@item and i.quantity>isnull(f.purchased, 0)
    order by i.id
    if @purchased is null break;
    insert into dbo.IncomingLinks(claim_id, incoming_id, quantity)
      values(@id, @incoming_id, @purchased);
    if @purchased=@rest break;
    set @rest=@rest-@purchased;
  end;
end;
close cr;
deallocate cr;

;with cte as (
  select
    l.id, l.item, l.created, l.quantity,
    l.quantity-isnull(f.purchased, 0) rest,
    row_number() over(partition by l.item order by l.created) priority
  from dbo.claims l
  outer apply (
    select sum(i.quantity)
    from dbo.IncomingLinks i
    where i.claim_id=l.id
  )f(purchased)
  where l.quantity-isnull(f.purchased, 0)>0
), Claims as (
  select
    t1.id, t1.item, t1.rest,
    isnull(sum(t2.rest), 0) + 1 as p_QuantityStart, isnull(sum(t2.rest), 0) + t1.rest as p_QuantityEnd
  from cte t1
  left join cte t2 on t2.item=t1.item and t2.priority<t1.priority
  group by t1.id, t1.item, t1.rest
), cte2 as (
  select
    i.id, i.item, i.quantity-isnull(f.[distributed], 0) rest,
    row_number() over(partition by i.item order by i.id) priority
  from dbo.Incomings i
  outer apply (
    select
      sum(l.quantity)
    from dbo.IncomingLinks l
    where l.incoming_id=i.id
  )f([distributed])
  where i.quantity-isnull(f.[distributed], 0)>0
), Incomings as (
  select
    t1.id, t1.item, t1.rest,
    isnull(sum(t2.rest), 0) + 1 as g_QuantityStart, isnull(sum(t2.rest), 0) + t1.rest as g_QuantityEnd
  from cte2 t1
  left join cte2 t2 on t2.item=t1.item and t2.priority<t1.priority
  group by t1.id, t1.item, t1.rest
)
insert into dbo.IncomingLinks(claim_id, incoming_id, quantity)
select
  p.id, g.id,
 case
  when p.p_QuantityStart >= g.g_QuantityStart and p.p_QuantityEnd <= g.g_QuantityEnd then p.rest
  when g.g_QuantityStart >= p.p_QuantityStart and g.g_QuantityEnd <= p.p_QuantityEnd then g.rest
  when g.g_QuantityStart between p.p_QuantityStart and p.p_QuantityEnd then p.p_QuantityEnd - g.g_QuantityStart + 1
  when g.g_QuantityEnd between p.p_QuantityStart and p.p_QuantityEnd then g.g_QuantityEnd - p.p_QuantityStart + 1
 end
from Claims p
join Incomings g on
  g.item=p.item and
  p.p_QuantityStart <= g.g_QuantityEnd and
  p.p_QuantityEnd >= g.g_QuantityStart
order by 1,2