How to query and output information from database as XML in C# in ASP.NET

If you don't actually need a string but read-only, processable XML, it's a 
better idea to use MemoryStream and XPathDocument:

XPathDocument result;
using (MemoryStream ms = new MemoryStream()) {
dataTable.WriteXml(ms);
ms.Position = 0;
result = new XPathDocument(ms);
}

Note that you can also directly create an XmlDataDocument from a DataSet 
(rather than a DataTable).

Select allOpen in new window

private static void ReadOrderData(string connectionString)
{
    string queryString = 
        "SELECT DBID,CUSTFNAME,CUSTLNAME,CUSTADDRESS,CUSTLAT,CUSTLON FROM YourTable;";
    string connectionString= "Server=(local);DataBase=Northwind;Integrated Security=SSPI";
    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        try
        {
           SqlDataAdapter daCustomers = new SqlDataAdapter(queryString , conn);
           daCustomers.Fill(dsCustomers, "Customers"); 

           string result;
           using (StringWriter sw = new StringWriter()) 
           {
              dsCustomers.Tables[0].WriteXml(sw);
              result = sw.ToString();
           }
        }
        finally
        {
        }
    }
}

Select allOpen in new window