如何在关联数组中获取所有帖子和PostMeta？

$allposts = $wpdb->get_results("
SELECT $wpdb->posts.post_title, $wpdb->postmeta.meta_key
FROM $wpdb->posts
JOIN $wpdb->postmeta 
ON $wpdb->postmeta.post_id = $wpdb->posts.id
WHERE $wpdb->posts.post_type = \'post\' AND $wpdb->posts.post_status =\'publish\';", OBJECT_K);