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

ALTER TABLE dbo.STOK ADD LOTGIRISIZORUNLU bit not null CONSTRAINT DF_STOK_LOTGIRISIZORUNLU DEFAULT 0
go