A Note on Security
If this is the first time you've worked with a Zope database connection, there's an important security point you may not have considered:
This means that you may not depend on the Plone content workflow to provide security for these connections and methods. You must use the Zope security mechanisms directly to control access.Zope Database Connections and Z SQL Methods are not part of the Plone workflow.
This is also true of Python scripts and other Zope-level objects you
might create via the ZMI. But Zope provides a safety net of security
for most of those. There is no such automatic safety net for external
RDBMS access methods.
The easiest way to do this is to use the ZMI to visit the top-most folder of your form and use the Security tab to customize security. Look in particular for the Use Database Methods permission, and make sure it is not extended to any user role that should not have a right to read or update your external database.