fetch data on pressing enter key

You can set AutoPostback property true, and call a method.like

<asp:TextBox ID="txtName" runat="server" Width="184px" AutoPostBack="True" ontextchanged=" txtName_TextChanged"></asp:TextBox>

and Method on code file would be

protected void txtName_TextChanged(object sender, EventArgs e)
   {
       //Data access logic
   }

another way......
The method described below allows you to submit when the user hits the enter key in a TextBox.

<input name="TextBox1" type="text" id="TextBox1" onkeypress="return clickButton(event,'button1')"  />

add javascript

function clickButton(e, button1){
      var evt = e ? e : window.event;
      var bt = document.getElementById(button1);
      if (bt){
          if (evt.keyCode == 13){
                bt.click();
                return false;
          }
      }
}

Hope this helps