怎么update blog字段

如何update blog字段
create   or   replace   procedure   load_blob(v_bdm   in   varchar2,v_blob_field   in   varchar2,
                                                                            v_where   in   varchar2,v_filename   in   varchar2)   is
    blob_loc   blob;
    bfile_loc   Bfile;
    amount   int;
    v_sql   varchar2(300);
begin
    v_sql:= 'select   '||v_blob_field|| '   from   '||v_bdm|| '   where   '||v_where|| '     for   update ';
    execute   immediate   v_sql   into   blob_loc   ;
    --create   or   ....DOWNFILE
    bfile_loc:=bfilename( 'DOWNFILE ',v_filename);
    dbms_lob.fileopen(bfile_loc,dbms_lob.file_readonly);
    amount:=dbms_lob.getlength(bfile_loc);
    dbms_lob.loadfromfile(blob_loc,   bfile_loc,amount);
    v_sql:= 'UPDATE   '||v_bdm|| '   SET   '||v_blob_field|| '   =   '||blob_loc|| '   WHERE   '||v_where;
    --PLS-00306:调用 '|| '时参数个数或类型错误
    execute   immediate   v_sql;
    dbms_lob.fileclose(bfile_loc);
end   load_blob;

执行时出的上面注释的问题,请问下blob字段可以这样更新吗.上面写的那个v_sql的语句中 "|| "不多也不少吧,为什么报这种错呢?

------解决方案--------------------
顶
------解决方案--------------------
for example:


--update BLOB
declare
a_blob BLOB;
bfile_name BFILE := BFILENAME( 'ULTLOBDIR ', 'log.txt ');
begin
update blobtest set col1=empty_blob() where rownum=1
returning col1 into a_blob;
dbms_lob.fileopen(bfile_name);
dbms_lob.loadfromfile(a_blob, bfile_name, dbms_lob.getlength(bfile_name));
dbms_lob.fileclose(bfile_name);
commit;
end;