ASP.NET

In this example I am Using AJAX to show how you can display data using AJAX.This will work very fast and you will see there is not page reload is occurring

Create a Web Application and modify Default.aspx html content
I am adding Script manager control and a Update Panel control, Under Update panel control add 2 labels and 2 dropdownlist control and gridview like below

Once Modify Default.aspx, open Default.aspx.cs and modify the Page_Load and add following code.

Now we will add code to fetch the Orders by particular Employee, for that we need write code in DropDownList1_SelectedIndexChanged event, please add following code

Now we will fetch the order details of selected order number for that we need to add the following code in DropDownList2_SelectedIndexChanged event

Now we are ready with over code, just build, run and test

Hope this help you.