Mysql group by top N

Mysql group by top N is frequently used to query the first few groups in daily work. in oracle, row_num can be used to support queries. mysql currently does not support row_num. how can we meet this requirement? For example, data in a table:

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

 

Expected results:

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

 

Method 1: Use row_num in oracle to add pseudo columns to SQL.

set @num := 0, @group := '';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;

 

Method 2: associate a subquery

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