Oracle groups fetch the first data in each group, and oracle groups

Oracle groups fetch the first data in each group, and oracle groups

select * from test;


No	Time	Name
1001	20141226	Zhangsan
1001	20141227	Lisi
1002	20141228	Wangwu
1002	20141229	Zhaoliu

select * from (select rank() over(partition by documentno order by time desc) r,a.* from test a) where r=1;
no time               name
-----     -----------      ----------  
1001     20141227        lisi
1002    20141229        zhaoliu