如何在 Oracle 中将 CLOB 转换为 BLOB?

Firstly I converted a BLOB of an image to CLOB, and then converted that CLOB back to BLOB. I cannot see the reconverted image. How can i solve this problem?

blob_to_clob 函数:

CREATE OR REPLACE FUNCTION blob_to_clob (blob_in IN BLOB) RETURN CLOB AS
  v_clob CLOB;
  v_varchar VARCHAR2(32767);
  v_start PLS_INTEGER := 1;
  v_buffer PLS_INTEGER := 32767;
BEGIN
  DBMS_LOB.CREATETEMPORARY(v_clob, TRUE);
  FOR i IN 1..CEIL(DBMS_LOB.GETLENGTH(blob_in) / v_buffer)
  LOOP
    v_varchar := UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.SUBSTR(blob_in, v_buffer, v_start));
    DBMS_LOB.WRITEAPPEND(v_clob, LENGTH(v_varchar), v_varchar);
    v_start := v_start + v_buffer;
  END LOOP;
  RETURN v_clob;
END blob_to_clob;

clob_to_blob 函数:

CREATE OR REPLACE FUNCTION clob_to_blob2(p_clob IN CLOB) RETURN BLOB IS
  v_blob BLOB;
  v_offset NUMBER DEFAULT 1;
  v_amount NUMBER DEFAULT 4096;
  v_offsetwrite NUMBER DEFAULT 1;
  v_amountwrite NUMBER;
  v_buffer VARCHAR2(4096 CHAR);
BEGIN dbms_lob.createtemporary(v_blob, TRUE);
  Begin
    LOOP
      dbms_lob.READ (lob_loc => p_clob,
        amount  => v_amount,
        offset  => v_offset,
        buffer  => v_buffer);

      v_amountwrite := utl_raw.length (r => utl_raw.cast_to_raw(c => v_buffer));

      dbms_lob.WRITE (lob_loc => v_blob,
        amount  => v_amountwrite,
        offset  => v_offsetwrite,
        buffer  => utl_raw.cast_to_raw(v_buffer));

      v_offsetwrite := v_offsetwrite + v_amountwrite;

      v_offset := v_offset + v_amount;
      v_amount := 4096;
    END LOOP;
  EXCEPTION
    WHEN no_data_found THEN
    NULL;
  End;
  RETURN v_blob;
END clob_to_blob2;

推荐答案

像这样的代码将执行最少的重新编码:

create or replace function clob2blob(AClob CLOB) return BLOB is
  Result BLOB;
  o1 integer;
  o2 integer;
  c integer;
  w integer;
begin
  o1 := 1;
  o2 := 1;
  c := 0;
  w := 0;
  DBMS_LOB.CreateTemporary(Result, true);
  DBMS_LOB.ConvertToBlob(Result, AClob, length(AClob), o1, o2, 0, c, w);
  return(Result);
end clob2blob;
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