Wie eindeutige Rechnungsnummer in DB erstellen und speichern?

[jobo]

Ich habe hier mal einen Versuch gemacht mit einer autarken SP ohne separates Reset des Generators. Da ich wenig Praxis mit FB habe, bitte gut testen. Vielleicht schaut ja auch einer der FB Kenner hier mal drüber.

SQL-Code:

-- create daily cyclic sequence number / expression 

-- table storing last used date
-- drop table rndatebuffer;
create table rndatebuffer (
  isRestricted char(1) Default 'X' unique,          --force one record only
  lastDate date not null ,
  constraint forceOneRow check (restricted='X'));   --force one record only
  
-- insert into rndatebuffer (lastdate) values(CURRENT_DATE-1);
-- select * from rndatebuffer;

-- sequence 
CREATE GENERATOR gen_rn;
SET GENERATOR gen_rn TO 0;


--drop procedure getrn;
--procedure to fetch new "number"
SET TERM ^ ;
CREATE Procedure GetRN RETURNS (prn varchar(20)) as
  declare aDif integer;
BEGIN

  select CURRENT_DATE-lastdate from rndatebuffer into :aDif;           -- detect date border
  if (aDif is null) then                                               -- init
  begin
    insert into rndatebuffer (lastdate) values(CURRENT_DATE);
    execute statement 'set generator gen_rn to 0';
  end

  If (aDif <> 0) then                                                  -- date border reached
  begin
    update rndatebuffer set lastdate=CURRENT_DATE;                     -- reset date buffer
    execute statement 'set generator gen_rn to 0';                     -- reset generator
  end

  for
    select                                                             -- build Rechnungsnummer 
      CAST(Extract(year FROM cast('NOW' as date))*10000 +
      Extract(month FROM cast('NOW' as date))*100 +
      Extract(day FROM cast('NOW' as date)) AS VARCHAR(8))||
      LPAD (gen_id(gen_rn,1), 6, '0') 
    from RDB$DATABASE into :prn
  do begin
    suspend;
  end
END
^

SET TERM ; ^

P.S.: der Aufruf wäre dann einfach

Code:

select * from GetRN;