set @artist = '';
set @num = 1;
select * from (
    select c.name,
           c.artist,
           @num := if(@artist = c.artist, @num + 1, 1) as row_number,
           @artist := s.artist as dummy
    from cds as c
) as results
where results.row_number <= 5;

##</code><code>##

my $rs = $schema->resultset('cds');
$rs = $rs->search({ genre => 'rock' });

##</code><code>##

$rs = $rs->limit_per_artist( 5 );