Select from multiple tables and make difference

Question

Line 2 or Line 3 alone working

 

I need to create column from multiple tables and sum...

Some help?

 

select naziv as 'Naziv artikla',
SUM (cast(kolicina as float)) as 'Nabavka' from (select naziv, kolicina from ulazni_racun_roba_roba union all select naziv, kolicina from mp_ulazni_racun_ostalo_roba) as alltables
SUM (cast(kolicina as float)) as 'Prodaja' from (select roba, kolicina from mp_racun_roba union all select roba, kolicina from mp_faktura_roba) as alltables
group by naziv

 I need result column:

1) Naziv artikla

2) Nabavka

3) Prodaja

4) Difference (Nabavka-Prodaja)