if not exists (select * from sys.syscolumns where name = 'IsAdd' and id = object_id(N'dbo.Subscription'))
    alter table dbo.Subscription
    add IsAdd bit not null constraint DF_Subscription_IsAdd default (1)
        ,IsEdit bit not null constraint DF_Subscription_IsEdit default (1)
        ,IsDelete bit not null constraint DF_Subscription_IsDelete default (1)
        ,Filter nvarchar(max) null
        ,FilterID uniqueidentifier null