> select NAME
> from (
> select RDB$CHARACTER_SET_NAME as NAME
> from RDB$CHARACTER_SETS
> )
>
> why occur error?

In general, this isn't called a "subselect" but a "derived table".

The current available stable version of Firebird (1.5) does not
support derived tables yet.

With regards,

Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL
Server.
Upscene Productions
http://www.upscene.com