fix outdated oscommerce shop problem. Uncaught Error: Call to undefined function mysql_connect()

dear friends

hope you are all well.

my oscommerce shop was outdated ,now I get this kind of problem whenever visiting this site.

I know its because of the old scripts doesnt support newest php7 and will try to update it later.but in the meantime,i hope to solve this problem to let the oscommerce shop run ,could you kindly help me to solve it ?

thanks.

Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /home/customer/www/mysite.com/public_html/catalog/includes/functions/database.php:19 Stack trace: #0 /home/customer/www/mysite.com/public_html/catalog/includes/application_top.php(65): tep_db_connect() #1 /home/customer/www/mysite.com/public_html/catalog/index.php(13): require('/home/customer/...') #2 {main} thrown in /home/customer/www/mysite.com/public_html/catalog/includes/functions/database.php on line 19