IF NOT EXISTS (SELECT * FROM SYSCOLUMNS INNER JOIN SYSOBJECTS ON SYSOBJECTS.id = SYSCOLUMNS.id 
WHERE SYSCOLUMNS.NAME = 'EFATURA_SGKPREFIKS' AND SYSOBJECTS.name = 'SUBELER') 
ALTER TABLE SUBELER ADD EFATURA_SGKPREFIKS nvarchar(3) NULL 
GO