PREPARE Stmt FROM
    'insert into posten select ' + cast(GetNewIndex(2) as Varchar) + ' 
as PostenID, '
     + cast(NewRechnungenID as Varchar) + ' as RechnungenID,OrderID, 
Datum, Ziffer, Begruendung,
     Uhrzeit, Faktor, Preis, Summe, Hoechstwert, Anzahl, 
BesondereKosten, Zeitstempel,HoechstwertPreis
     from Posten where RechnungenID = ?';
  Execute Stmt using RechnungenID;

GetNewIndex is this function (short version):

FUNCTION "GetNewIndex" (IN "Tablenumber" INTEGER)
RETURNS INTEGER
BEGIN
DECLARE Result CURSOR FOR Stmt;
DECLARE NewIndex INTEGER DEFAULT -1;

  PREPARE Stmt FROM
    'Update indizes set ID = ID + 1 where Tablenumber = ?';
  Execute Stmt using Tablenumber;
  PREPARE Stmt FROM
    'Select ID from indizes where Tablenumber = ?';
  OPEN Result using Tablenumber;
  Fetch FIRST FROM Result(ID) INTO NewIndex;

RETURN NewIndex;
END