IF NOT EXISTS (SELECT * FROM SYSCOLUMNS INNER JOIN SYSOBJECTS ON SYSOBJECTS.id = SYSCOLUMNS.id 
               WHERE SYSCOLUMNS.NAME = 'DONEMBASI' AND SYSOBJECTS.name = 'FATURA')
BEGIN
ALTER TABLE dbo.FATURA add
 	[DONEMBASI] [datetime] NULL,
	[DONEMSONU] [datetime] NULL,
	[EVRAKREFNO] [nvarchar](25) NULL,
	[MUKELLEFKODU] [nvarchar](50) NULL,
	[MUKELLEFADI] [nvarchar](50) NULL
END
GO