This tag has a long and complicated historically. It predates our use of Phabricator (it imported from Bugzilla), and therefore also predates our use of workboards and (mostly) predates the decentralised triaging of incoming tasks on a per-project or per-team basis.
Back then it was all a shared pile in Bugzilla where were all manage it collectively as a single engineering department, with the components primarily serving the needs of end-users who would reporting issues and express the area with some keywords and a (single) sub component of "MediaWiki".
The "Database" component would then be used for whenever something needed maintenance on WMF db servers, or when a third-party site-admin encountered an issue setting up or migrating their database, or when end-users encounter internal server errors that relate to a database in some way. Anything that had some relation to a database.
I don't think this is useful anymore in this form. It doesn't serve any of the relevant audiences well.
* For end-users reporting an issue with a feature they tried to use, the chances of a product owner finding the bug report here are next to nil.
* For bugs and proposals for core schema changes, we have #Schema-change already.
What remains is issues with the Wikimedia-Rdbms library, which is what the majority of open issues on this workboard are currently about.
I propose to:
* Hide "Schema change" column, untag issues and ensure #Schema-change is present instead, as well as at least one relevant MediaWiki-prefixed component tag (or #MediaWiki-General).
* Hide "Usage problem" column. After a while, untag or migrate to a new generic tag if there's interest.
* Rename project to Wikimedia-Rdbms.