select sysdate from dual; --当前时间  2016/9/7 10:32:04

select trunc(sysdate) from dual;--取当天  2016/9/7

select trunc(sysdate,‘yyyy‘) from dual; --取当年第一天  2016/1/1

select trunc(sysdate,‘mm‘) from dual; --取当月第一天  2016/9/1

select trunc(sysdate,‘dd‘) from dual; --取当天 2016/9/7

select trunc(sysdate,‘d‘) from dual; --返回当前星期的第一天  2016/9/4

select trunc(sysdate,‘hh‘) from dual; --返回当前时间，精确到小时  2016/9/7 10:00:00

select trunc(sysdate,‘mi‘) from dual; --返回当前时间，精确到分钟 2016/9/7 10:32:00

select trunc(2016.11) from dual; --2016

select trunc(2016.99) from dual; --2016

select trunc(2016.99,1) from dual; --2016.9

select trunc(2016.99,3) from dual; --2016.99

select trunc(2016.99,-1) from dual; --2010

select trunc(2016.99,-2) from dual; --2000

select trunc(2016.99,-4) from dual; --0

select trunc(2016,1) from dual; --2016

select trunc(2016,-1) from dual; --2010