declare @df varchar(200)
select @df=name from sysobjects where name like 'DF__BBX1__BBX47__%'
if isnull(@df,'')>''
exec('alter table BBX1 drop '+@df)
if exists(select * from syscolumns where id=OBJECT_ID('BBX1') and name='BBX47')  
alter table BBX1 alter column BBX47 varchar(128) null