add.sql

if not exists (SELECT * FROM sysobjects INNER JOIN syscolumns ON 
    sysobjects.id = syscolumns.id 
    WHERE sysobjects.name = N'Test' AND syscolumns.name = N'xxx')
ALTER TABLE [dbo].[Test] ADD xxx NVARCHAR(MAX)


ALTER TABLE [dbo].[Test] 
DROP COLUMN xxx;

----------------------

IF COL_LENGTH('dbo.Test', 'xxx') IS  NULL
BEGIN
   ALTER TABLE [dbo].[Test] ADD xxx NVARCHAR(MAX)
END