Query meta key WP

SELECT p.* FROM wp_posts p
        LEFT JOIN wp_postmeta pm ON p.ID = pm.post_id
        LEFT JOIN wp_term_relationships tr ON p.ID = tr.object_id
        LEFT JOIN wp_terms t ON t.term_id = tr.term_taxonomy_id
        WHERE  (p.id IN (SELECT pm.post_id FROM wp_postmeta pm WHERE pm.meta_key = 'anno' AND pm.meta_value = '2012'))
        AND  p.post_type = 'impianti' AND p.post_status = 'publish'
        GROUP BY p.ID