title: ORA-01843: not a valid month : TO_DATE('12-JUN-02','DD-MON-YY')
body: <p>I've faced a problem during insert. Here is the problem: </p>
  
  <pre><code>INSERT INTO SALES_ORDER_A4 (ORDERNO , CLIENTNO , ORDERDATE , DELYADDR , SALESMANNO , DELYTYPE , BILLYN , DELYDATE, ORDERSTATUS)
  SELECT 'O19008' ,
         'C00005' ,
         to_date('24-MAY-02','DD-MON-YY'),
         'Delhi' ,
         'S00004' ,
         'F' ,
         'N' ,
         to_date('26-MAY-02','DD-MON-YY') ,
         'In Process'
  FROM DUAL
  UNION ALL
  SELECT 'O19001' ,
         'C00001' ,
         to_date('12-JUN-02','DD-MON-YY') ,
         'Delhi' ,
         'S00001' ,
         'F' ,
         'N' ,
         to_date('20-JUN-02','DD-MON-YY') ,
         'In Process'
  FROM DUAL
  UNION ALL
  SELECT 'O19002' ,
         'C00002' ,
         to_date('25-JUN-02','DD-MON-YY'),
         'Delhi' ,
         'S00002' ,
         'P' ,
         'N' ,
         to_date('27-JUL-02','DD-MON-YY') ,
         'Cancelled'
  FROM DUAL
  </code></pre>
  
  <hr>
  
  <p>I have faced an exception at  phrase *to_date('12-JUN-02','DD-MON-YY' )* that: </p>
  
  <blockquote>
    <p>ORA-01843: not a valid month</p>
  </blockquote>
  
  <p>My instructor can not find the problem, what is the problem here?</p>