mysql limit inside group?

Question

I want to limit the size of records inside a group, and here is my trial, how to do it right?

mysql> select * from accounts limit 5 group by type;
         


        

Answer 1

I've had some luck with using numbered rows:

set @type = '';
set @num = 0;

select
  items.*,
  @num := if(@type = item_type, @num + 1, 1) as dummy_1,
  @type := item_type as dummy_2,
  @num as row_number
from items
group by
  item_type,
  row_number
having row_number < 3;

This will give you 2 results per item_type. (One gotcha: make sure you re-run the first two set statements otherwise your row numbers will steadily get higher and higher and the row_number < 3 restriction won't work.

I pieced this together from a couple of posts which have been linked in other answers on SO.