select p.filename, group_concat(n.name)
from pindex_photos p
left join pindex_link l on l.photo_id = p.id
left join pindex_names n on l.name_id = n.id
group by p.filename
and
select n.name, group_concat(p.filename)
from pindex_photos p
left join pindex_link l on l.photo_id = p.id
left join pindex_names n on l.name_id = n.id
group by n.name