SPSiteDataQuery class

You can use an instance of this class to retrieve data from selected lists or from all lists in the current site collection. Specify the scope of the query by setting the Webs property. Specify the lists to participate in the query by setting the Lists property and the fields to return by setting the ViewFields property. Control data selection and order by setting the Query property.

To execute the query, pass the SPSiteDataQuery object to the GetSiteData(SPSiteDataQuery) method, which returns a DataTable object containing rows of data that represent the result of the query. Each DataRow object in the DataTable.Rows collection represents a single item that satisfies the query. Each DataColumn object in the DataTable.Columns collection represents a field that is requested in the ViewFields property, and the column name equals the value of the Name attribute for that field. In addition, the data table contains a column named WebId, which identifies the Web site that contains each item, a column named ListId, which identifies the list that contains each item, and a column named ID, which identifies each item.

The following example is a Web Part that queries all lists that were created with the Contacts list template anywhere in the site collection, retrieves the first and last names of every contact, and displays that information in a GridView control.

Note that if you compile the example code, you can deploy the Web Part simply by copying the compiled assembly to the bin directory of the Web application. If you choose that method of deployment, be sure your project includes a reference to Microsoft.SharePoint.Security.dll. Then add the Web Part to the SafeControls list in the web.config file and elevate the Web application's trust level to WSS_Medium. For more information, see Deploying Web Parts in Windows SharePoint Services and Securing Web Parts in Windows SharePoint Services.

Caution
The enumeration value for Contacts is 105.

Reference