First of all: Thank you guys for all the inputs!!
So, I see that nobody uses a separate table mantained with triggers to do that,
which make think I won't have any performance issues if I construct the current
account "on the fly". I Like the idea of "closing a year" but some customers are
reluctant to do that, so I would use it as a general rule for al my systems.

May I ask a couple more questions?

> Views can be used for the balance of which you speak and they can can be
> very fast.
> Alan

I can't figure out how can make it with a view. I mean how a view would help me
to show the balance column, which depends on the previous record. May I have an
example, please?

> Two possible approaches to calculating the running balance per record
> that you could look at are:
> a) use a 'selectable stored procedure' (& calculate the running balance
> balance per record therein),
> b) use the caller (Delphi, VB, Crystal Reports etc) to calculate the running
> balance component of the query.
> HTH,
> John

I think I will use a SP, because if I calculate the balance on the client side
and want to show it in a non unidirectional query (ie: in a grid) I don't know
how to calculate the balance. I imagine I can have a calculated field to select
the previous record and take the previous balance from there, but I wouldn't
know how to do it nor like the idea! Am I right? or there is a "proper" way to
do that?

Thanks again guys!

-s