select case when 的用法

题目1.  日期    结果
2009-05-09   胜
2009-05-09   胜
2009-05-09   负
2009-05-09   负
2009-05-10   胜
2009-05-10   负
2009-05-10   负
怎么用SQL语句输出或者查询出
2009-05-09 2胜2负
2009-05-10 1胜2负
要SQL语句

create table myrs(
id int primary key,
dodate date,
rs varchar(32)
);
insert into myrs values(1, '2009-05-09', '胜');insert into myrs values(2, '2009-05-09', '胜');insert into myrs values(3, '2009-05-09', '负');insert into myrs values(4, '2009-05-09', '负');insert into myrs values(5, '2009-06-09', '胜');insert into myrs values(6, '2009-06-09', '负');insert into myrs values(7, '2009-06-09', '负');insert into myrs values(8, '2009-06-09', '负');

select dodate,sum(case when rs='胜' then 1 else 0 end)+'胜'+sum(case when rs='负' then 1 else 0 end) +'负'
from myrs
group by dodate;