blob2clob/clob2blob研究

一。两种方法实现



blob到clob的转换

CREATE OR REPLACE FUNCTION blob2clob(v_blob_in IN BLOB) RETURN CLOB IS

  v_file_clob    CLOB;
  v_file_size    INTEGER := dbms_lob.lobmaxsize;
  v_dest_offset  INTEGER := 1;
  v_src_offset   INTEGER := 1;
  v_blob_csid    NUMBER := dbms_lob.default_csid;
  v_lang_context NUMBER := dbms_lob.default_lang_ctx;
  v_warning      INTEGER;
  v_length       NUMBER;

BEGIN

  dbms_lob.createtemporary(v_file_clob, TRUE);

  dbms_lob.converttoclob(v_file_clob,
                         v_blob_in,
                         v_file_size,
                         v_dest_offset,
                         v_src_offset,
                         v_blob_csid,
                         v_lang_context,
                         v_warning);

  RETURN v_file_clob;

EXCEPTION
  WHEN OTHERS THEN
    dbms_output.put_line('Error found');

END;
/

CREATE OR REPLACE FUNCTION blob2clob(b BLOB) RETURN CLOB IS
  c CLOB;
  n NUMBER;
BEGIN
  IF (b IS NULL) THEN
    RETURN NULL;
  END IF;
  IF (length(b) = 0) THEN
    RETURN empty_clob();
  END IF;
  dbms_lob.createtemporary(c, TRUE);
  n := 1;
  WHILE (n + 32767 <= length(b)) LOOP
    dbms_lob.writeappend(c,
                         32767,
                         utl_raw.cast_to_varchar2(dbms_lob.substr(b,
                                                                  32767,
                                                                  n)));
    n := n + 32767;
  END LOOP;
  dbms_lob.writeappend(c,
                       length(b) - n + 1,
                       utl_raw.cast_to_varchar2(dbms_lob.substr(b,
                                                                length(b) - n + 1,
                                                                n)));
  RETURN c;
END;

会出现错误的地方

1.如果转换的blob文件长度为0则会报错   ORA-22994: 源偏移量超出源 LOB 的结尾

2. offset是in out参数，第一次传入后会被更改，如果是loop处理。应该将其值重新初始化。否则会报错ora-22994

如下

declare
  v_cl         clob;
  dest_offset  integer := 1;
  src_offset   integer := 1;
  lang_context integer := dbms_lob.default_lang_ctx;
  warning      integer;
begin
  for pr in (select pr_id, cmms_log
               from purchase_requisition
              where dbms_lob.getlength(cmms_log) > 0) loop
    dbms_lob.createtemporary(lob_loc => v_cl, cache => false);
    dbms_lob.convertToClob(dest_lob     => v_cl,
                           src_blob     => pr.cmms_log,
                           amount       => dbms_lob.lobmaxsize,
                           dest_offset  => dest_offset,
                           src_offset   => src_offset,
                           blob_csid    => dbms_lob.default_csid,
                           lang_context => lang_context,
                           warning      => warning);
    --dbms_output.put_line(warning);
    update purchase_requisition
       set cmms_log_clob = v_cl
     where pr_id = pr.pr_id;
  end loop;
  --commit;
  rollback;
exception
  when others then
    rollback;
    dbms_output.put_line('更新出错：' || sqlcode || ';' || sqlerrm);
end;

正确应该是

declare
  v_cl         clob;
  dest_offset  integer := 1;
  src_offset   integer := 1;
  lang_context integer := dbms_lob.default_lang_ctx;
  warning      integer;
begin
  dbms_output.put_line('开始执行');
  for pr in (select pr_id, cmms_log
               from purchase_requisition
              where dbms_lob.getlength(cmms_log) > 0) loop
    dbms_output.put_line(pr.pr_id);
    dest_offset  := 1;
    src_offset   := 1;
    lang_context := dbms_lob.default_lang_ctx
    dbms_lob.createtemporary(lob_loc => v_cl, cache => false);
    dbms_lob.convertToClob(dest_lob     => v_cl,
                           src_blob     => pr.cmms_log,
                           amount       => dbms_lob.lobmaxsize,
                           dest_offset  => dest_offset,
                           src_offset   => src_offset,
                           blob_csid    => dbms_lob.default_csid,
                           lang_context => lang_context,
                           warning      => warning);
    dbms_output.put_line(warning);
    update purchase_requisition
       set cmms_log_clob = v_cl
     where pr_id = pr.pr_id;
  end loop;
  commit;
exception
  when others then
    rollback;
    dbms_output.put_line('更新出错：' || sqlcode || ';' || sqlerrm);
end;

二。clob到blob的转换

同一，将函数换成 dbms_lob.converttoblob即可