Oracle获得当前系统时间

select sysdate from dual
select to_char(sysdate,'yyyy-MM-dd HH24:mi:ss') from dual;
select to_char(sysdate,'yyyy-MM-dd HH24:mm:ss') from dual;
select to_char(sysdate,'yy-mm-dd hh24:mi:ss') from dual

select TO_CHAR(SYSDATE,'YY/MM/DD HH24:MI:SS')
from dual;

select user from dual