group by trunc(createtime, 'DD'))

//按自然周统计 
select to_char(date,'iw'),sum() 
 from  tablename
 group by to_char(date,'iw') 
 //按自然月统计 
select to_char(date,'mm'),sum() 
 from   tablename
 group by to_char(date,'mm') 

 //按季统计 
select to_char(date,'q'),sum() 
 from  tablename
 group by to_char(date,'q') 

 //按年统计 
select to_char(date,'yyyy'),sum() 
 from  tablename
 group by to_char(date,'yyyy')

转载自：http://blog.csdn.net/u011659172/article/details/40186009