"Duilio Foschi" <dedalus@...> wrote in message
news:3.0.1.32.20020227004408.006c2adc@......

> is it possible to change all fields of type A into fields of type B in a
> database by _wisely_ modifying the system tables ?

If you operate through DDL (alter table -> alter column) it will allow only
changes that are safe. For example, you can't shrink a column. You would get
a run-time error about string truncation if there are values that filled
completely the original column's length.
When you write to system tables, you bypass DDL and DYN. After that, I hope
you know how wise you can be.

> I mean: will IB take care of all due casting of the field containt ?

Yes, but it's a performance penalty. You better backup and restore after
such changes. Another one is to do a dummy update followed by a select * but
with gbak you will know effectively if your db survived the change when you
try to restore.

C.
--
Claudio Valderrama C. - http://www.cvalde.com - http://www.firebirdSql.org
Independent developer
Owner of the Interbase® WebRing