There are some Android apps out there that claim connectivity and querying functionality for Oracle, MySQL, or SQL Server.

http://www.appszoom.com/android_applications/business/mysql-sql-client_bbwxj.html

There is a Microsoft JDBC Driver for SQL Server:

http://msdn.microsoft.com/en-us/sqlserver/aa937724

Also several 3rd party open source providers:

jTDS JDBC Driver

http://jtds.sourceforge.net/