问如何将F983051.VRPODATA (long / blob)转换为字符串(varchar2)？

EN

SELECT DBMS_LOB.SUBSTR({Huge Blob Field}) FROM {Table};

CREATE TABLE F983051 (vrpid NUMBER, vrvers NUMBER, vrpodata BLOB) 
  LOB (vrpodata) STORE AS SECUREFILE;

INSERT INTO F983051(vrpid, vrvers, vrpodata) 
VALUES (1, 2, rawtohex('Hello world'));

CREATE OR REPLACE FUNCTION myblobtovarchar(p_blob BLOB) 
  RETURN VARCHAR2 DETERMINISTIC
IS
  l_len          number;
  l_clob         clob;
  l_dest_offsset integer := 1;
  l_src_offsset  integer := 1;
  l_lang_context integer := dbms_lob.default_lang_ctx;
  l_warning      integer;
  l_varchar      varchar2(32767);
BEGIN
  IF p_blob IS NULL THEN RETURN NULL; END IF;

  DBMS_LOB.CREATETEMPORARY(lob_loc => l_clob, cache => false);

  l_len := DBMS_LOB.GETLENGTH(p_blob);

  IF l_len > 4000 THEN l_len := 4000; END IF;

  DBMS_LOB.CONVERTTOCLOB(dest_lob     => l_clob,
                         src_blob     => p_blob,
                         amount       => l_len,
                         dest_offset  => l_dest_offsset,
                         src_offset   => l_src_offsset,
                         blob_csid    => dbms_lob.default_csid,
                         lang_context => l_lang_context,
                         warning      => l_warning);

  l_varchar := DBMS_LOB.SUBSTR(l_clob, 32767, 1);

  RETURN l_varchar;
END myblobtovarchar;
/

SELECT vrpid, vrvers, myblobtovarchar(vrpodata) FROM F983051;
1   2   Hello world

SELECT utl_raw.cast_to_varchar2(dbms_lob.substr(vrpodata, 4000)) FROM F983051;