Remove customers who did not place any orders

DELETE from wp_users where wp_users.ID not in (
SELECT meta_value FROM wp_postmeta WHERE meta_key = '_customer_user'
) AND wp_users.ID not in (
select distinct(post_author) from wp_posts

Author: Wojciech Borowicz

I hope this post will help you to do what you need.
In case you want some assistance click here to get in touch 

check out other blog posts