来自http://tunps.com/wordpress-delete-post_type-revision-post
DELETE a,b,c
FROM wp_posts a
LEFT JOIN wp_term_relationships b ON (a.ID = b.object_id)
LEFT JOIN wp_postmeta c ON (a.ID = c.post_id)
WHERE a.post_type = 'revision';
跨表delete，sql语句来自http://www.ludou.org/wordpress-post-id-continuous.html