insert into mrp (comptype, lowlevel, itemid,qty,st)
select 2,0,itemid,qty,0 from saleorder

declare @n int
set @n = 0
while exists (select itemid from mrp where st = 0 )
begin
-- Raw materials

insert into mrp (comptype, lowlevel, itemid,qty,st)
select 1, @n, b.compid, b.compqty*p.qty/b.partqty,1
from mrp p inner join bom b on b.partid = p.itemid 
where p.st=0 and b.comptype = 1

-- products 

insert into mrp (comptype, lowlevel, itemid,qty,st)
select 2, @n+1, b.compid, b.compqty*p.qty/b.partqty,0
from mrp p inner join bom b on b.partid = p.itemid 
where p.st=0 and b.comptype = 2

update mrp set st=1 where lowlevel = @n
set @n = @n + 1

end