Select values frow both query MS SQL

Question

I have good code, but need to repair them
Item code, name, Third column is procurement, fourth column is sale, and last column i difference (5) (column 3-column 4)
In my code result is just item if have in procurement

CASE 1
Exmp Coca cola
Procurement 5
Sale 3
Result 2
That is ok, problem is next.

CASE 2
If I not procure Coca Cola need to be next
Procurement 0
Sale 2
Result -2

In my code result is empty in CASE 2

Thanks for help

 

 

SELECT x1.sifra                                              AS 'Šifra',
       x1.naziv                                              AS 'Naziv',
       CONVERT(DECIMAL(16, 2), Sum(Isnull(x1.nabavka, 0)))   AS 'Nab. (kol.)',
       CONVERT(DECIMAL(16, 2), Sum(Isnull(x2.prodaja, 0)))   AS 'Prod. (kol.)',
       CONVERT(DECIMAL(16, 2), Sum(CONVERT(DECIMAL(16, 2), x1.nabavka) - (
                                   Isnull(x2.prodaja, 0) ))) AS 'Stanje (kol.)'
FROM  (SELECT naziv,
              sifra,
              Sum(Isnull(kolicina, 0)) AS Nabavka
       FROM  (SELECT naziv                    AS naziv,
                     sifra,
                     Sum(Isnull(kolicina, 0)) AS kolicina
              FROM   popis_roba
              GROUP  BY naziv,
                        sifra) a
       GROUP  BY naziv,
                 sifra) x1
      LEFT JOIN(SELECT roba,
                       sifra,
                       Sum(Isnull(kolicina, 0)) AS Prodaja
                FROM  (SELECT roba,
                              sifra,
                              Sum(Isnull(kolicina, 0)) AS kolicina
                       FROM   mp_racun_roba
                       GROUP  BY roba,
                                 sifra) b
                GROUP  BY roba,
                          sifra) x2
             ON x2.roba = x1.naziv
WHERE  x1.naziv IS NOT NULL
GROUP  BY x1.naziv,
          x1.sifra