After upgrading to PHP 7 or higher you may encounter the following error:
SQL ERROR [ mysql4 ]
mysql_connect function does not exist, is mysql extension installed? 
An sql error occurred while fetching this page. Please contact an administrator if this problem persists.
The reason for this is the mysql request is deprecated in the new version of PHP, as part of the security update to 7 from 5.6.40. All that needs to be done is to modify the configuration file and switch the configuration file from “mysql” to “mysqli” as the method for requesting the database.