In certain circumstances you may want to update the database instead of querying it for data. The query tag will accept an update query and update the target data source. The value attribute of the tag becomes the number of rows affected by the update query.
The data source refers to the default data source of the tag provider as opposed to the default data source of the project.
In the Gateway Configure Section, go to Tags > Realtime and edit the appropriate tag provider. Set the default database connection that this tag provider will use for its query tags.