how to change the default date format in oracle New to Oracle here, i am working on some assigments but i noticed when i was creating the tables using a script, oracle throws the following error:

ORA-01858: a non-numeric character was found where a numeric was expected
01858. 00000 -  "a non-numeric character was found where a numeric was expected"
*Cause:    The input data to be converted using a date format model was
       incorrect.  The input data did not contain a number where a number was
       required by the format model.
*Action:   Fix the input data or the date format model to make sure the
       elements match in number and type.  Then retry the operation.


knowing that the date format in my queries is something like '01-JUN-2012'
i was wondering how can i change the default format in my oracle installation to meet my system format? I am using SQL Developer with the Free Oracle version 11g.

also i am wondering if this is because my computer is WIN 7 french version and teh dates in my queries are in the English US format?

UPDATE bb_product
   set salestart = '01-JUN-2012', saleend = '15-JUN-2012', SalePrice = 8.00
   WHERE idProduct = 6;


this query is from the Brewer Beans DB that my professor handed out. an which i am assuming was created in a system that uses the EN-US format...any help?
You generally don't want to rely on implicit conversions of strings to dates.  That only leads to pain and suffering since different users will have different date formats.  Either use ANSI date literals or use the to_date function with an explicit format mask

UPDATE bb_product
   SET salestart = date '2012-06-01',
       saleend   = date '2012-06-15',
       saleprice = 8
 WHERE idProduct = 6


or

UPDATE bb_product
   SET salestart = to_date('01-JUN-2012', 'DD-MON-YYYY'),
       saleend   = to_date('15-JUN-2012', 'DD-MON-YYYY'),
       saleprice = 8
 WHERE idProduct = 6