oracle中date类型转换和比较大小

oracle中date类型转换和比较大小：    select created from user_objects where created > to_date('2012-04-26','YYYY-MM-DD');    CREATED    ---------    10-MAY-12    10-MAY-12    05-JUN-12    05-JUN-12    05-JUN-12 1. 日期和字符转换函数用法（to_date,to_char）select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') as nowTime from dual;   //日期转化为字符串