title: How can I fix this error 'ORA-01843: not a valid month'
body: <p>I am trying to create a table using the followning query: </p>
  
  <pre><code>create table customer1
  (
  custmer_id number, 
  Customer_name varchar(20), 
  Expiry_date  date default TO_DATE ('31-12-2009','dd-mon-RR')
  )
  </code></pre>
  
  <p>the result is the following error : </p>
  
  <pre><code>Error report -
  ORA-01843: not a valid month
  01843. 00000 -  "not a valid month"
  *Cause:    
  *Action:
  </code></pre>
  
  <p>Anyone to give me a light regarding this.
  Thank you.</p>