IF NOT EXISTS (SELECT * FROM SYSCOLUMNS INNER JOIN SYSOBJECTS ON SYSOBJECTS.id = SYSCOLUMNS.id 
               WHERE SYSCOLUMNS.NAME = 'ZORHAVAYOLUVAR' AND SYSOBJECTS.name = 'HYATIS')

ALTER TABLE dbo.HYATIS ADD  ZORHAVAYOLUVAR bit not null CONSTRAINT DF_HYATIS_ZORHAVAYOLUVAR DEFAULT 0
go