MySQL Regular Expressions | newbie tutorial
https://www.runoob.com/mysql/mysql-regexp.html
(1 message) used regular expressions - mail (Email) - Samuel - CSDN blog
https://blog.csdn.net/make164492212/article/details/51656638
PHP regular expressions mail | newbie tutorial
https://www.runoob.com/w3cnote/php-email-regrex.html