email
------------------------
 user0@gmail.com
 user10000000@gmail.com
 user10000001@gmail.com
 user10000002@gmail.com
 user10000003@gmail.com
 user10000004@gmail.com
 user10000005@gmail.com
 user10000006@gmail.com
 user10000007@gmail.com
 user10000008@gmail.com

email
------------------------
 user0@gmail.com
 user1@gmail.com
 user2@gmail.com
 user3@gmail.com
 user4@gmail.com
 user5@gmail.com
 user6@gmail.com
 user7@gmail.com
 user8@gmail.com
 user9@gmail.com

SELECT email FROM acc_denorm
ORDER BY TO_NUMBER(REGEXP_SUBSTR(email, 'user(d+)@gmail.com', 1, 1, '', 1))