SQL> select systimestamp from dual;

SYSTIMESTAMP

--------------------------------------------------------------------------------

21-OCT-15 09.57.06.491638 AM +08:00

SQL> select systimestamp+0 from dual; --oracle会自动进行隐式转换

SYSTIMESTAMP+0

--------------

2015-10-21 9:5

SQL> select cast(systimestamp as date) from dual;

CAST(SYSTIMESTAMPASDATE)

------------------------

2015-10-21 9:57:28