Just how useful may this be? If each table has some audit columns named: date_created, date_last_update, created_by and updated_by, then the whole idea of natural join crumbles, for the system would "naturally" (!) try to join using the audit columns. Wouldn't it? So this thing I find rather an useless complication: inner join, left/right join and full outer join should suffice for any developer. Moreover, for quite some years I've been developing on Oracle without using left/right, but using the old Oracle syntex with (+), which I intend to continue using as long as I can, for it is quite simple.