Try to add in left join UNION ALL
SELECT naziv AS 'Naziv', SUM(Kol_potr_repromat) AS 'Sum_Kol_potr_repromat' FROM ( SELECT t.naziv, t.kolicina * SUM(s.kolicina) AS 'Kol_potr_repromat' FROM dbo.normativi_roba t LEFT JOIN normativi_lista k ON t.id_fakture = k.id LEFT JOIN ( SELECT * FROM DBO.mp_racun_roba a WHERE s.roba IN (SELECT naziv FROM dbo.roba_usluge WHERE podgrupa_artikala = 'HRANA') UNION ALL select * from mp_faktura_roba a -- ON k.naziv = a.roba WHERE a.roba IN (SELECT naziv FROM dbo.roba_usluge WHERE podgrupa_artikala = 'HRANA') ) ON k.naziv = a.roba AND k.naziv = a.roba GROUP BY t.naziv, t.jedinica_mjere, t.kolicina ) AS SubqueryAlias GROUP BY naziv;
Errorin line 21:
Incorrect syntax near the keyword 'ON'.