On Tue, 09 Apr 2013 10:51:43 -0300, Gugui
<gugui_sarubi_macchi@...> wrote:

> hi Marijn,
>
> i´m using firebird-server-classic-2.1.3.18185.0-5mdv2010.0

Alter table for computed fields was added in Firebird 2.5:
http://www.firebirdsql.org/file/documentation/reference_manuals/reference_material/html/langrefupd25-ddl-table.html#langrefupd25-alter-table

Mark