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.
As many are aware, the hosting industry has been upgrading PHP to its latest version of 7.3.3 for additional security. Many of the original themes that have not been updated contain code that is only compatible with PHP 5.6.40.
This fix applies to RocketTheme WordPress Templates but may also apply to others as well. Part of the Rockettheme core contains RokCommon components. If you have recently upgraded from PHP 5.6.40 to PHP 7.* you may experience a blank page for WordPress after the upgrade.
The fix is to
- Download the latest RokCommon Core here: https://rockettheme.com/wordpress/plugins/rokutilities
- Once the zip file has been downloaded, unzip the file and locate the “wp_RokCommon” folder.
- Upload all of these files to your WordPress plugin directory located in: (Your WordPress Install Directory)\wp-content\plugins\wp_rokcommon\
- Overwrite the existing files. This will fix the incompatibility issue, when you refresh the site it should now be live and functioning on PHP 7.3.3.