方法2：采用join

SELECT COUNT(1)
FROM
(
SELECT *
FROM
 (SELECT user_id AS i FROM user_order WHERE creat_date = '2018-5-22' GROUP BY user_id) a
 LEFT JOIN
 (SELECT user_id AS m FROM user_order  WHERE creat_date  < '2018-5-22' GROUP BY user_id) b
ON a.i = b.m
WHERE b.m IS NULL) t