Recurring script can be used to run some script that need to executed whenever we issue php bin/magento setup:upgrade irrespective of version change.
The recurring script will be run after the module setup script every time the command line
php bin/magento setup:upgrade
This script will be defined same as InstallSchema class but difference in name of the class. The example for this class you can see in vendor/magento/module-indexer/Setup/Recurring.php
Some time its necessary to create DB tables and add data to tables. Mageto provides some classes using which you can create DB table structure or add data to tables. Following are the important classes
InstallSchema – This class can be used to setup DB structure when modules is instaled for the first time.
InstallData – This class can be used to load the initial data when modules is insttale for the first time. Continue reading SQL Setup Script Magento 2