We just changed the default "send mail from" address, so I want to easily see whether there are any projects that are using a non-default address. We have several hundred projects, and I don't want to visit all of them.
Update: Thanks to Boris's answer, I determined this query:
SELECT pname, propertyvalue
FROM propertyentry
JOIN propertystring USING (ID) JOIN project ON ENTITY_ID = project.ID
WHERE PROPERTY_KEY = 'jira.project.email.sender' AND propertyvalue IS NOT NULL