oracle trunc函数截取日期

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