title: Not a valid month in oracle when add_months is used
body: <p>I have given the below code in query.</p>
  
  <pre><code>    where to_date(cal_wid,'yyyymmdd') 
      between  add_months(to_date(sysdate, 'MM-YYYY'),-12) 
      and      to_date(sysdate, 'MM-YYYY')
  </code></pre>
  
  <p>I am getting the following bug. (I am doing in a Xampp server)</p>
  
  <pre><code>   Warning: oci_execute(): ORA-01843: not a valid month in C:\xampp\htdocs\xxx\index.php on line 149
  
     Warning: oci_fetch_array(): ORA-24374: define not done before fetch or execute and fetch in C:\xampp\htdocs\xxx\index.php on line 160
  </code></pre>
  
  <p>Can anyone tell why I am getting this error?</p>