From OpenEMR Project Wiki
Note this page is for developers to describe the patch process. For actual Patches, go to the OpenEMR Patches wiki page. And for the steps on how to release a offical patch, go to the Steps for a patch release wiki page.
This is currently rather simple and involves a step to update the codebase and a step to update the database.
All new code is carried over to a release branch (ie. rel-xxx) and all files that have been modified are intermittently packaged in a zip file. So, can upgrade code by patching from the rel-xxx branch or by patching from the packaged zip file.
The sql_patch.php script will upgrade database, globals, and the version/patch (from version.php script). It loads the database changes from the sql/patch.sql file.(note also add database changes to database.sql in case users install from the rel-xxx branch)