Number of SQL statements grouped by age group

The SQL statement counts the number of people by age group. Java code www.2cto.com create table # t (Uname varchar (10), age int) insert # t select 'Ah', 19 union all select 'info ', 23 union all select 'baby', 31 union all select 'hour', 21 union all select 'mimi', 6 select nnd as 'age', count (*) as 'number of people' from (select case when age> = 1 and age <= 10 then'1-10' when age> = 11 and age <= 20 then'11-20' when age> = 21 and age <= 30 then '21-30' when age> = 31 and age <= 40 then '31-40' end as nnd, uname from # t) a group by nnd