declare
   c1 clob := to_clob('abc');
   c2 clob;
 begin
      case c1
          when to_clob('abc') then dbms_output.put_line('abc');
          when to_clob('def') then dbms_output.put_line('def');
      end case;

      c2 := case c1
        when to_clob('abc') then 'abc'
         when to_clob('def') then 'def'
     end;
      dbms_output.put_line(c2);
end;