title: Oracle dynamic sql
body: <p>Why this code doesn output result?  Write PL/SQL procedure successfully completed. and that all</p>
  <pre><code>declare 
    count_train    number(20); 
    v_query_str varchar2(255);
   begin 
    v_query_str :=  'select count(*) from TRAIN';
    execute immediate  v_query_str
    into count_train;
    Dbms_output.put_line(count_train);
   end; 
  </code></pre>