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="customposttype"
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="customposttype"