+ my $cols = "ref, array_to_string(form || alt, '/'), prio, id, sub";
+ %rows = $db->select(_word => $cols, \%filter)->map_arrays;
+ defined $_->[-1] or pop @$_ for values %rows;
+ $rows{''} = [
+ (undef) x 3,
+ [$db->select(word => 'id', {cat => undef, ref => undef})->flat]
+ ];
+ say pp \%rows