Oracle guid、declare

declare newguid VARCHAR2(50); 
begin
  for c in (select * from bcd_samplingrecord where recordid is null)
    loop
      SELECT lower(SUBSTR(GUID,1,8))||'-'||lower(SUBSTR(GUID,9,4))||'-'||lower(SUBSTR(GUID,13,4))||'-'||lower(SUBSTR(GUID,17,4))||'-'||lower(SUBSTR(GUID,20,12)) into newguid
FROM 
(
    SELECT SYS_GUID() GUID  FROM DUAL
);
      update bcd_samplingrecord set recordid=newguid,samplingtype=0 where id= c.id;
      insert into bcd_samplingrecord_detail(
                                            recordid,
                                            samplingdate,
                                            sampling_stime,
                                            sampling_etime,
                                            filter_mode,
                                            filterid,
                                            hasfilter)
      values(newguid,c.sampling_date,c.sampling_stime,c.sampling_etime,0,c.filter_number,c.hasfilter);
    end loop;
end;