We understand that not everyone can operate in a Full Trust environment.  At 21 Concepts, we are working to determine which databases work well (or at all) in medium trust. The limiting factor is, of course, the ADO.NET Data Provider that is used to connect to your database. Often these Data Providers are written by the community (in the case of open source databases) or by the database manufacturer (like DB2 or Sybase), so determining if these providers work in medium trust or not is the key.

Database System	Minimum Trust Requirements	Note
Microsoft SQL Server (all versions)	Medium
Microsoft Access (Microsoft Jet)	Full	* could not get this working with OleDbPermission and Medium Trust
Advantage Data Architect	Not Tested
Sybase SQL Anywhere	Not Tested
Sybase Adaptive Server Enterprise	Not Tested
IBM DB2	Not Tested
Firebird	Medium w/ modification Full w/o modification	Firebird .NET Provider must be recompiled to allow partially trusted callers Firebird .NET Provider must be installed in the GAC The web_mediumtrust.config must be modified to allow FirebirdClientPermission With enough interest, we can provide the re-compiled Firebird .NET provider
SQL Server Mobile	Medium
MySql	Medium w/ modification Full w/o modification	The web_mediumtrust.config must be modified to allow SocketPermission
Oracle	Medium
Pervasive	Not Tested
PostgreSQL	Full	* .NET provider probably can be recompiled to allow partially trusted callers. With enough interest, we can provide.
SQLite	Medium*	* System.Data.SQLite must be installed in the global assembly cache
VistaDB	Medium

Some of the ADO.NET Data providers for specific databases (Firebird, PostgreSQL) have been compiled without the required [AllowPartiallyTrustedCallers()] attribute, which means that they could *never* work in a medium trust environment. Documentation suggests that PostgreSQL's ADO.NET data provider CAN be recompiled to allow partially trusted callers without any problems. We cannot find supporting documentation for Firebird, but are planning to test in the near future.  If you have any knowledge about the untested providers above, Please let us know!

For a detailed list of ADO.NET Data Providers and Database systems supported by 21 Providers, please see 21 Providers Database Systems Supported