Ronaldo,

r> |-----------------------------------|
r> | Order(Position) | order_id |
r> |-----------------------------------|
r> | 1 | 1 |
r> | 2 | 5 |
r> | 3 | 3 |
r> |-----------------------------------|

I tend to do this kind of things on the client side, for the sake of
efficiency (why download predictable data such as a counter) and/or
added flexibility.
This may or may not apply to your situation depending on the client
environment you are using.

The way I know of doing it server side is through a selectable stored procedure.

Ciao
--
Nando mailto:nandod@...