Oracle not using index when > used in where clause
Oracle should be able to use the statistics to determine the high and low values for any column if you are keeping them up to date:

drop table foo;
create table foo(id date primary key);
insert into foo select sysdate-level from dual connect by level&lt;31;
select low_value, high_value from dba_tab_columns where table_name='FOO';
/*
LOW_VALUE                                    HIGH_VALUE
-------------------------------------------- ------------------------------------------ 

*/
execute dbms_stats.gather_table_stats('JDOUGLAS', 'FOO');
select low_value, high_value from dba_tab_columns where table_name='FOO';
/*
LOW_VALUE                                    HIGH_VALUE
-------------------------------------------- ------------------------------------------
786F0C0A0E0837                               787001080E0837
*/