CREATE PROCEDURE PROC_NOVA_SIFRA_GEN(GEN VARCHAR(50))
RETURNS (SIF BIGINT)
AS
begin
if(not exists( select 1 from RDB$GENERATORS where
RDB$GENERATOR_NAME=:GEN)
) then execute statement 'CREATE GENERATOR ' || :GEN;

execute statement 'select GEN_ID('|| :GEN ||',1) from RDB$DATABASE'
into :SIF;

suspend;
end