IF NOT EXISTS (SELECT * FROM SYSCOLUMNS INNER JOIN SYSOBJECTS ON SYSOBJECTS.id = SYSCOLUMNS.id 
               WHERE SYSCOLUMNS.NAME = 'DRISYERITESISKODU' AND SYSOBJECTS.name = 'TDRKIMLIK')
ALTER TABLE TDRKIMLIK ADD DRISYERITESISKODU nvarchar(15) NULL