Why the SQL Monitor report do not display?

Question

Why the SQL Monitor report do not display?
SQL> set serveroutput on
SQL> variable my_rept CLOB;
SQL> BEGIN
  2  :my_rept :=DBMS_SQLTUNE.REPORT_SQL_MONITOR();
  3  END;
  4  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.93
SQL> print :my_rept
MY_REPT
SQL Monitoring Report
SQL>

Answer 1

You can you hint /*+MONITOR*/, and then use this procedure to display the monitor report:
SQL> select /*+ monitor */ *from hr.employees where salary>10000;
SQL> variable my_rept CLOB;
SQL> BEGIN
  2  :my_rept :=DBMS_SQLTUNE.REPORT_SQL_MONITOR();
  3  END;
  4  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:01.21
SQL> print :my_rept
MY_REPT
SQL Monitoring Report
SQL Text
select /*+ monitor */ *from hr.employees where salary>10000
Global Information
Status              :  DONE (ALL ROWS)
Instance ID         :  1
Session ID          :  170
MY_REPT
SQL ID              :  4tj5p5m6qrkmp
SQL Execution ID    :  16777216
Plan Hash Value     :  1445457117
Execution Started   :  04/30/2010 10:51:23
First Refresh Time  :  04/30/2010 10:51:23
Last Refresh Time   :  04/30/2010 10:51:23
| Elapsed |  Other   | Fetch | Buffer |
| Time(s) | Waits(s) | Calls |  Gets  |
...