Delete WordPress users with no posts by MySQL query

Back up your database regularly, and always before any upgrade. This query delete wordpress users (and they meta info) with no posts:

##delete meta info of user with no posts
DELETE FROM wp_usermeta
where user_id NOT IN (
	SELECT post_author
	FROM wp_posts
	GROUP BY post_author
);

##delete user with no posts
DELETE FROM wp_users
where ID NOT IN(
	SELECT post_author
	FROM wp_posts
	GROUP BY post_author
);

This query select users with no posts:

SELECT u.* 
FROM wp_users u
LEFT JOIN wp_posts p ON u.ID = p.post_author
WHERE p.ID IS NULL
GROUP BY u.ID

This query select users with no posts and no comments:

SELECT u.* 
FROM wp_users u
LEFT JOIN wp_posts p ON u.ID = p.post_author
LEFT JOIN wp_comments c ON u.ID = c.user_id
WHERE p.ID IS NULL AND c.comment_ID IS NULL
GROUP BY u.ID;