select convert(varchar(10),addtime , 120) addtime,
  sum(case when len(username) > 1 then 1 else 0 end) type1,
  sum(case when len(username) = 1 then 1 else 0 end) type2
from tb
group by convert(varchar(10),addtime , 120)

------解决方案--------------------
SQL code
select convert(varchar(10),addtime , 120) addtime,
  count(case when len(username) > 1 then 1  end) type1,
  count(case when len(username) = 1 then 1  end) type2
from tb
group by convert(varchar(10),addtime , 120)

------解决方案--------------------
SQL code
create table tb(userid int, username varchar(10) , addtime datetime)
insert into tb values(11 , 'abc', '2008-8-8 11:20:30') 
insert into tb values(12 , 'a'  , '2008-8-8 11:21:30') 
insert into tb values(13 , 'a'  , '2008-8-8 11:31:30') 
insert into tb values(14 , 'a'  , '2008-8-9 11:50:30') 
go

select convert(varchar(10),addtime , 120) addtime,
  sum(case when len(username) > 1 then 1 else 0 end) 'type1(长度大于1)',
  sum(case when len(username) = 1 then 1 else 0 end) 'type2(长度等于1)'
from tb
group by convert(varchar(10),addtime , 120)

drop table tb

/*
addtime    type1(长度大于1) type2(长度等于1) 
---------- ------------ ------------ 
2008-08-08 1            2
2008-08-09 0            1

（所影响的行数为 2 行）
*/