select d.id,
  coalesce(t1.txtname, t2.txtitem) txtitem,

  t1.purch_price,
  t1.sale_price,
  t1.limit,
  t1.firstbalance,
 sum(t2.qty) as 'purchaseqty'

from
(
  select  id from item
  union
  select  iditem from inv_sub,inv WHERE  inv.id = inv_sub.no and inv.type = 'شراء'

) d
left join item t1
  on d.id = t1.id
left join inv_sub t2
  on d.id = t2.iditem
  GROUP BY d.id,t2.iditem