select * from customer c where TRUNC (TO_DATE(c.create_time,'yyyy-mm-dd hh24:mi:ss')) >
add_months(to_date('20130216','yyyy-mm-dd'),-6);
select * from customer c where TRUNC (TO_DATE(c.create_time,'yyyy-mm-dd hh24:mi:ss')) >
add_months(to_date('20130216','yyyy-mm-dd'),-6);