SharePoint SPSiteDataQuery

SPSiteDataQuery is used to Query multiple lists or to read data from all the lists in 

a site collection.

Get Combined result

Below is the example to query multiple list data sources and get combined information in data table:

using (SPSite site = new SPSite(pSiteUrl))
{
     using (SPWeb web = site.OpenWeb())
     {
                        // Fetch using SPSiteDataQuery
                        SPSiteDataQuery query = new SPSiteDataQuery();

                        query.Lists = "<Lists MaxListLimit=\"5\">" +
                              "<List ID=" + web.Lists.TryGetList("Announcements").ID + " />" +
                              "<List ID=" + web.Lists.TryGetList("Content and Structure Reports").ID + " />" +
                              "<List ID=" + web.Lists.TryGetList("NavigationList").ID + " />" +
                              "<List ID=" + web.Lists.TryGetList("Reusable Content").ID + " />" +
                           "</Lists>";

                        query.ViewFields = "<FieldRef Name=\"Title\" />";
                        query.Webs = "<Webs Scope=\"Web\" />";
             
                        //Write appropriate query
                        query.Query = "";

                        query.RowLimit = 10;

                        //Convert result collection to data table

                        DataTable dataTable = web.GetSiteData(query);
           }
}

Reference:

https://msdn.microsoft.com/en-us/library/microsoft.sharepoint.spsitedataquery.aspx

https://msdn.microsoft.com/en-us/library/ee539975.aspx