Sample Code using DataTable and spsitedataquery.

using System;
using System.Data;
using Microsoft.SharePoint;
//using Microsoft.SharePoint.Library;
using Microsoft.SharePoint.Administration;
namespace ConsoleApplication2
{
class ConsoleApplication2
{
static void Main(string[] args)
{
using (SPSite site = new SPSite("http://prasad.bolla3.sharepointsite.net/"))
{
using (SPWeb web = site.OpenWeb())
{
SPSiteDataQuery query = new SPSiteDataQuery();
// Get IDs for all fields used in the query.
string assignedToId = SPBuiltInFieldId.AssignedTo.ToString("B");
string taskDueDateId = SPBuiltInFieldId.TaskDueDate.ToString("B");
string titleId = SPBuiltInFieldId.Title.ToString("B");
string taskStatusId = SPBuiltInFieldId.TaskStatus.ToString("B");
string percentCompleteId = SPBuiltInFieldId.PercentComplete.ToString("B");
// Define the data selection.
string where = "";
where += "";
where += "";
where += "";
// Define the sort order.
string orderBy = "";
orderBy += "";
orderBy += "";
// Set the query string.
query.Query = where + orderBy;
// Query task lists.
query.Lists = "";
// Specify the view fields.
query.ViewFields = "";
query.ViewFields += "";
query.ViewFields += "";
query.ViewFields += "";
// Query all Web sites in this site collection.
query.Webs = "";
// Run the query.
DataTable results = web.GetSiteData(query);
// Print the results.
Console.WriteLine("{0, -10} {1, -30} {2, -30} {3}", "Date Due", "Task", "Status", "% Complete");
foreach (DataRow row in results.Rows)
{
// Extract column values from the data table.
string dueDate = (string)row[taskDueDateId];
string task = (string)row[titleId];
string status = (string)row[taskStatusId];
string percentComplete = (string)row[percentCompleteId];
// Convert the due date to a short date string.
DateTime dt;
bool hasDate = DateTime.TryParse(dueDate, out dt);
if (hasDate)
dueDate = dt.ToShortDateString();
else
dueDate = String.Empty;
// Convert the PercentComplete field value to a percentage.
decimal pct;
bool hasValue = decimal.TryParse(percentComplete, out pct);
if (hasValue)
percentComplete = pct.ToString("P0");
else
percentComplete = "0 %";
// Print a line.
Console.WriteLine("{0, -10} {1, -30} {2, -30} {3, 10}", dueDate, task, status, percentComplete);
}
}
}
Console.ReadLine();
}
}
}