create or alter procedure SYS$GETUNUSEDGEN
returns (
    UNUSED_GEN_NAME varchar(32),
    GEN_VALUE bigint)
AS
begin
  /* получить список неиспользуемых генераторов и их значения */
  for select rdb$generators.rdb$generator_name
      from rdb$generators
      where (rdb$generators.rdb$system_flag is null or rdb$generators.rdb$system_flag=0)
      into :unused_gen_name
  do begin
       if (not exists(select rdb$dependencies.rdb$dependent_name
                      from rdb$dependencies
                      where rdb$dependencies.rdb$depended_on_name=:unused_gen_name
                            and rdb$dependencies.rdb$depended_on_type=14)) then
           begin
             execute statement 'SELECT GEN_ID('||:unused_gen_name||',0) AS GEN_VALUE FROM RDB$DATABASE' INTO :gen_value;
             suspend;
           end
     end
end