Oracle: DBMS_LOB.CREATE_TEMPORARY

create table tq84_temporary_clob(c clob);

declare
   c_   clob;
begin
   dbms_lob.createtemporary(c_, false);

   dbms_lob.append(c_, 'foo');
   dbms_lob.append(c_, 'bar');
   dbms_lob.append(c_, 'baz');

   insert into tq84_temporary_clob values (c_);

   dbms_lob.freetemporary(c_);
end;
/

select * from tq84_temporary_clob;

drop table tq84_temporary_clob;