oracle存储过程将字段CLOB转成BLOB

CREATE OR REPLACE FUNCTION C2B(b IN CLOB default empty_clob()) RETURN BLOB
-- typecasts BLOB to CLOB (binary conversion)
 IS
  res          BLOB;
  b_len        number := dbms_lob.getlength(b);
  dest_offset1 NUMBER := 1;
  src_offset1  NUMBER := 1;
  amount_c     INTEGER := DBMS_LOB.lobmaxsize;
  blob_csid    NUMBER  := DBMS_LOB.default_csid;
  lang_ctx     INTEGER := DBMS_LOB.default_lang_ctx;
  warning      INTEGER;
BEGIN
  if b_len > 0 then
    DBMS_LOB.createtemporary(res, TRUE);
    DBMS_LOB.OPEN(res, DBMS_LOB.lob_readwrite);
    DBMS_LOB.convertToBlob(res,
                           b,
                           amount_c,
                           dest_offset1,
                           src_offset1,
                           blob_csid,
                           lang_ctx,
                           warning);
 
  else
    select empty_blob() into res from dual;
  end if;
  RETURN res; -- res is OPEN here
END C2B;