MySQL 取分类后的前n条

select *

from (SELECT @num:=0,@AAA:= 0) temp join

(

   select 

   @num := if(@AAA = AAA, @num + 1, 1) as row_number,

   @AAA := AAA as Dummy,

   mt.* 

  from table1 mt 

  where Created_Time BETWEEN DATE_SUB(CURRENT_TIMESTAMP,INTERVAL 1 DAY) and CURRENT_TIMESTAMP 

  order by AAA, ID desc

) as x where x.row_number <= 3;