---------- Original Message -----------
From: "Ismael L. Donis Garcia" <ismael@...>

> As I could validate that an alone field of varchar(11) enabled numbers
> and that these had 11 characters of length?

------- End of Original Message -------

http://www.firebirdsql.org/refdocs/langrefupd25-similar-to.html

I've not used FB regular expressions yet, but my first stab would be:

alter table ... add constraint ... check (value similar to '[[:DIGIT:]]{11}');


-Philip