if not exists (select name from dbo.syscolumns where id=object_id('vldCampaign') and name = N'CO')
    begin
        alter table vldCampaign add CO int default '3'
        update vldCampaign set CO = '3' 
    end
go

R>решение, конечно, гениально простое, но сервер посылает тебя еще на проверке синтаксиса..

if not exists (select name from dbo.syscolumns where id=object_id('vldCampaign') and name = N'CO')
begin
  alter table vldCampaign add CO int default '3'
end
go
update vldCampaign set CO = '3' where CO is NULL

S>if not exists (select name from dbo.syscolumns where id=object_id('vldCampaign') and name = N'CO')
S>begin
S>  alter table vldCampaign add CO int default '3'
S>end
S>go
S>update vldCampaign set CO = '3' where CO is NULL
S>

GO is not a Transact-SQL statement; it is a command recognized by the osql and isql utilities and SQL Query Analyzer.