1、获取系统时间的语句(ssxff6获取小数点后面六位)?
select sysdate,systimestamp,to_char(systimestamp, 'yyyymmdd hh24:mi:ssxff6'),?
? to_char(systimestamp, 'yyyymmdd hh24:mi:ss.ff6') from dual;??

2、字符型转成timestamp?
select to_timestamp('2011-09-14 12:52:42.123456789', 'syyyy-mm-dd hh24:mi:ss.ff') from dual;?

3、timestamp转成date型?
select cast(to_timestamp('2011-09-14 12:52:42.123456789', 'syyyy-mm-dd hh24:mi:ss.ff') as date) timestamp_to_date from dual;??

4、date型转成timestamp?
select cast(sysdate as timestamp) date_to_timestamp from dual;??

5、两date的日期相减得出的是天数，而两timestamp的日期相减得出的是完整的年月日时分秒小数秒?
select sysdate-sysdate,systimestamp-systimestamp from dual;?

select extract(day from inter) * 24 * 60 * 60 +???
? extract(hour from inter) * 60 * 60 + extract(minute from inter) * 60 +???
??? extract(second from inter) "seconds" from?
(?
? select to_timestamp('2011-09-14 12:34:23.281000000', 'yyyy-mm-dd hh24:mi:ss.ff') -???
??? to_timesta