Pl/Sql Trigger for changing default date format in oracle -

i want ensure every time logon date format changed '24-apr-2014' '24/04/2014'

for created pl/sql trigger follows

    create or replace trigger change_date_format     after logon on database     begin     alter session set nls_date_format = 'mm/dd/yyyy';     end;     / 

however not logged on sysdba perhaps thats why error

    sql> @c:/pl/datetrigger.sql     after logon on database            *     error @ line 2:     ora-01031: insufficient privileges 

what can ensure date format changed permanently?

your error means not allowed create such trigger. on wrong track. must set default @ database level.

setting default datetime format template

from oracle documentation

the default datetime format template specified either explicitly initialization parameter nls_date_format or implicitly initialization parameter nls_territory. can change default datetime formats session alter session statement.

then case format must set in database initialization parameters.

to check have right value in current session:

select value v$parameter upper(name)='nls_date_format';