# untested
my %results;
while (my $data = $sth->fetchrow_hashref()) {
    while (my($k, $v)= each %$data) {
        push( @{$results{$k}}, $v );
    }
}
# your dataplot should then go like this:
@data_to_plot = ( [ @results{qw/dayofweek canning multipack quest/} ] );