>
> I want in one select show flags for every unit separeted with
> the colon. Is it possible? I do not know how...

Good news is the function already exists and it's called LIST. The bad news
is it's availble in FB 2.1 that is in beta at the moment.
But you can implement it with stored procedure, something similiar was
posted by Adam a couple of hours ago in another thread...

> So I am thinking about write own aggregate function.
> Is it possible to define own aggregate function (instead of
> COUNT something like MERGESTRING) in the Firebird?
>

You can't write your own aggregate functions

Sasha