> EXECUTE STATEMENT is for executing queries only, your code is not just a
> query as it contains an IF statement. I think for your purposes you need
> to use EXECUTE BLOCK
> http://www.firebirdsql.org/file/documentation/reference_manuals/reference_material/html/langrefupd25-execblock.html

Thanks Mark!

Yes... I've been reading it before, but I didn't found any example similar of what I want to do...

Perhaps is no possible at all?

Anyway, I was "inspired" in a firebird FAQ

http://www.firebirdfaq.org/faq133/