The module sqldiff config file allows for updates to the datamodel for a module. This is an outdated way to do things, modules should now use the liquibase.xml way in modules.
The file is checked on every startup of the module. The child diff tags are iterated over in a top down fashion. The earliest diff should be at the top and the most recent diff should be at the bottom. Each "diff" element is executed one at a time. As each one runs, the "version" is stored in a Global Property in the user's database: moduleid.database_version. The next time the module is started, ONLY "diff"s that have a "version" GREATER THAN the version stored in the moduleid.database_version will be run. This allows for easy upgrading for module users and module devs don't need to worry about who has what version.
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