数据库的group by 分组

有一个表 

查询结果为

用下面的代码写

select COUNT( case NumName  when 'a' then NumName  end ) as 'aaa',
 COUNT( case NumName when 'b' then NumName end )  as 'bb',
 COUNT( case NumName when 'c' then NumName  end) as 'cc'
from dbo.DataTb