1.select trunc(sysdate) from dual 
2.select trunc(sysdate, ‘mm‘)  from dual 
3.select trunc(sysdate,‘yy‘) from dual 
4.select trunc(sysdate,‘dd‘) from dual 
5.select trunc(sysdate,‘yyyy‘) from dual 
6.select trunc(sysdate,‘d‘) from dual 
7.select trunc(sysdate, ‘hh‘) from dual  
8.select trunc(sysdate, ‘mi‘) from dual 

oracle trunc函数截取日期