oracle 触发器，拆单，求问

Question

 CREATE OR REPLACE TRIGGER SPLITSINGLETRIGGER
  BEFORE INSERT ON CT_CUS_GDSHOPGUIDBILLENTRY
  FOR EACH ROW
DECLARE
  V_NEWID VARCHAR2(50);
  V_NUMBER VARCHAR2(50);
BEGIN
  SELECT FID
    INTO V_NEWID
    FROM CREFID
   WHERE FSTATE = 1
     AND ROWNUM = 1;
      SELECT ABS(MOD(DBMS_RANDOM.RANDOM,50)) INTO V_NUMBER FROM DUAL;
  IF :NEW.FSEQ >= 2 THEN
    --当选择的商品数大于等于2 ，给表头插入新的一条数据
    INSERT INTO CT_CUS_GDSHOPGUIDBILL
      SELECT FCREATORID,
             FCREATETIME,
             FLASTUPDATEUSERID,
             FLASTUPDATETIME,
             FCONTROLUNITID,
             FNUMBER || TO_CHAR(V_NUMBER), --修改FNUMBER
             FBIZDATE,
             FHANDLERID,
             FDESCRIPTION,
             FHASEFFECTED,
             FAUDITORID,
             FSOURCEBILLID,
             FSOURCEFUNCTION,
             V_NEWID, --修改FID
             FFIVOUCHERED,
             CFFICOMPANYID,
             CFGUIDERNAMEID,
             CFGUIDERNAMESHOW,
             CFGUIDERID,
             CFBILLTYPE,
             CFBILLSTATE,
             CFSGBILLSTATES,
             CFGDSHOPGUIDERNUM,
             CFORGANIZATIONUNIT,
             CFAUDITDATE,
             CFDELIVERYORDER,
             CFCONFIRM,
             CFTOREVIEWDATE,
             CFCONFIRMDATE,
             CFTOREVIEW,
             FENTITYCUSTOMER,
             FENTITYCUSTOMERADDRESS,
             FENTITYCUSTOMERTEL,
             CFBUSFEEDBACK,
             CFFINFEEDBACK,
             CFYANZHENGMA,
             CFOSMDANHAO
        FROM CT_CUS_GDSHOPGUIDBILL
       WHERE FID = :NEW.FPARENTID;
    :NEW.FPARENTID := V_NEWID;
    :NEW.FSEQ      := 1;
    UPDATE CREFID SET FSTATE = 2 WHERE FID = V_NEWID;--修改state
  END IF;
END;

触发器现在是生成随机数，不过还是FNUMBER有可能会重复
提交商品不止一个的话本来是想给fnumber加上一个有顺序的数字
比如拆两条，有一条fnumber+2
拆三条，一条+2，一条+3
但是传过来的fseq（本来是序号）可能由于先拆两单，再拆导致序号不固定，
出现重复的fnumber，有什么办法，让fnumber可以按顺序来，

Answer 1

如果不想他重复且自动累加，可以借助oracle 的序列sequence，定义个序列，每次获取nextval