Ho risolto mettendo diversi inner e usando gli alias
SELECT * FROM ot_posts INNER JOIN ot_postmeta AS m1 ON ( ot_posts.ID = m1.post_id ) INNER JOIN ot_postmeta AS m2 ON ( ot_posts.ID = m2.post_id ) WHERE ot_posts.post_type = 'iscritti' AND ( m1.meta_key = 'nominativo') AND ( m2.meta_key = 'indirizzo') GROUP BY ot_posts.ID ORDER BY ot_posts.post_title ASC;p.s. come faccio a mettere il topic risolto?