WordPress database error: [Deadlock found when trying to get lock; try restarting transaction]
UPDATE wp0t_mailpoet_subscribers s JOIN wp0t_usermeta as wpum ON s.wp_user_id = wpum.user_id AND wpum.meta_key = 'last_name' SET s.last_name = SUBSTRING(wpum.meta_value, 1, 255) WHERE s.last_name = '' AND s.wp_user_id IS NOT NULL AND wpum.meta_value IS NOT NULL