This feature contains the Microsoft JDBC Driver For SQL Server (com.microsoft.sqlserver.jdbc.SQLServerDriver) which is distributed under a non-open source proprietary license.
KNIME Analytics Platform 4.6 Update Site, Version 4.6.0
http://update.knime.com/analytics-platform/4.6
In case you can’t install the extension via drag & drop, please check that the update site is activated.