最近在移植的时候需要处理blob和varchar的相互转换，借鉴了别人的思路，写了2个函数，给大家分享下：

--varchar_to_blob
create or replace function varchar_to_blob(v_char in varchar2) 
return blob
is
 v_blob blob;
 v_start int:=1;
 v_buffer int:=400;
begin
 if dbms_lob.getlength(v_char) is null then 
     return utl_raw.cast_to_raw(''); 
  else
     print dbms_lob.getlength(v_char)/v_buffer;
    for j in 1..ceil(length(v_char)) loop
        v_blob:=utl_raw.cast_to_raw(dbms_lob.substr(v_char,v_start,1));
        v_start:=v_start+1;
     end loop;
     return v_blob;
   end if;
end varchar_to_blob;

--BLOB_TO_VARCHAR
Create or Replace function BLOB_TO_VARCHAR (v_blob in blob) return varchar2
is
v_varchar varchar2(4000);
v_start int:=1;
v_buffer int:=4000;
begin
	if dbms_lob.getlength(v_blob) is null then
		return '';
	else
		for j in 1..ceil(dbms_lob.getlength(v_blob)) loop
			v_varchar:=utl_raw.cast_to_varchar2(dbms_lob.substr(v_blob,v_start,1));
			v_start:=v_start+1;
		end loop;
		return v_varchar;
	end if;
end blob_to_varchar;