Mysql group by top N的问题_MySQL

+--------+-------+-----+| Person | Group | Age |+--------+-------+-----+| Bob    | 1     | 32  || Jill   | 1     | 34  || Shawn  | 1     | 42  || Jake   | 2     | 29  || Paul   | 2     | 36  || Laura  | 2     | 39  |+--------+-------+-----+

+--------+-------+-----+| Shawn  | 1     | 42  || Jill   | 1     | 34  || Laura  | 2     | 39  || Paul   | 2     | 36  |+--------+-------+-----+

set @num := 0, @group := &#39;&#39;;select person, `group`, agefrom (   select person, `group`, age,      @num := if(@group = `group`, @num + 1, 1) as row_number,      @group := `group` as dummy  from mytable  order by `Group`, Age desc, person) as x where x.row_number <= 2;

SELECT a.person, a.group, a.age FROM person AS a WHERE (SELECT COUNT(*) FROM person AS b WHERE b.group = a.group AND b.age >= a.age) <= 2 ORDER BY a.group ASC, a.age DESC