how to calcuate the time taken to execute the query?

Stopwatch sw = Stopwatch.StartNew(); 
// Your query here
sw.Stop(); 
TimeSpan ts = sw.Elapsed;

// Format and display the TimeSpan value.
string elapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}",
ts.Hours, ts.Minutes, ts.Seconds,
ts.Milliseconds / 10);
Console.WriteLine("RunTime " + elapsedTime);