Sumed all which has been summed
you can use the WITH ROLLUP in the group by to achieve multi level aggregation. try something like this SQL Fiddle

create table table1
(
register_time date,registered int  
);

insert into table1 values('2015/03/31',10);
insert into table1 values('2015/03/31',20);
insert into table1 values('2015/03/21',30);
insert into table1 values('2015/02/01',15);
insert into table1 values('2015/02/01',1);
insert into table1 values('2015/02/02',25);
insert into table1 values('2015/01/31',11);


SELECT MONTH(ds.register_time) Month,DAY(ds.register_time) day,SUM(registered) AS totalOftheDay
  FROM table1 ds
  GROUP BY MONTH(ds.register_time),DAY(ds.register_time) WITH ROLLUP