Create view inv_info as
Select distinct a.invnumber as Inv, a.transdate, ct.customernumber as Cust, ct.name, p.partnumber as Part,
i.description, i.qty, p.unit, p.weight, i.sellprice, (i.qty*i.sellprice)::numeric(7,0)as Subtotal
from invoice i, ar a, parts p, customer ct
where a.id = i.trans_id
and p.id = i.parts_id
and a.customer_id = ct.id
and i.sellprice >0;