difference between item template and layout template - asp.net

Question

what is the difference between item template and the layout template. in layout template only we have information about the designing? or any thing else. i am unable to understand the item template.. please explain..!
In addition to this one i have query in project like this
SELECT TOP (1) ProductName, UnitPrice FROM Products ORDER BY NEWID()
here NEWID() means what? is it predefined function related to sqlserver? there is no any newid() function in my project which was downloaded. if it is predefined function then what it can do?
Thank you

Answer 1

The main layout of a ListView control is created by defining a LayoutTemplate. The LayoutTemplate will include controls that acts as a placeholder for the data like Table, Panel, Label or HTML controls like table, div, or span elements that have a runat attribute set to "server".
Item template is the main template which will show the data bounded to the ListView in a repeated manner. This template typically contains controls that are data-bound to data columns or other individual data elements. These two templates are mandatory.
GroupTemplate will be used to group the items. The EditItemtemplate, SelectedItemTemplate, InsertItemTemplate are shown at that particular operation like insert, edit, select. ItemSeparatorTemplate, GroupSeparatorTemplate are used to separate the individual items and group Items Separately.
Here this makes difference ItemPlaceholderID="itemPlaceholder"
<asp:ListView runat="server" ID="ListView1" ItemPlaceholderID="itemPlaceholder">
<LayoutTemplate>
<table border="0" cellpadding="1">
<tr style="background-color:#E5E5FE">
<th align="left"><asp:LinkButton ID="lnkId" runat="server">Id</asp:LinkButton></th>
<th align="left"><asp:LinkButton ID="lnkName" runat="server">Name</asp:LinkButton></th>
<th align="left"><asp:LinkButton ID="lnkType" runat="server">Type</asp:LinkButton></th>
<th></th>
</tr>
<tr id="itemPlaceholder" runat="server"></tr>
</table>
</LayoutTemplate>
<ItemTemplate>
<tr>
<td><asp:Label runat="server" ID="lblId"><%#Eval("ID") %></asp:Label></td>
<td><asp:Label runat="server" ID="lblName"><%#Eval("FirstName")+"
"+Eval("LastName") %></asp:Label></td>
<td><asp:Label runat="server" ID="lblType"><%#Eval("Type") %></asp:Label></td>
<td></td>
</tr>
</ItemTemplate>
<AlternatingItemTemplate>
<tr style="background-color:#EFEFEF">
<td><asp:Label runat="server" ID="lblId"><%#Eval("ID") %></asp:Label></td>
<td><asp:Label runat="server" ID="lblName"><%#Eval("FirstName")+" "+
Eval("LastName") %></asp:Label></td>
<td><asp:Label runat="server" ID="lblType"><%#Eval("Type") %></asp:Label></td>
<td></td>
</tr>
</AlternatingItemTemplate>
</asp:ListView>
Reference links: reference site, code project reference

Answer 2

It looks like you're using the ListView control.
The ItemTemplate property only applies to the data item bound to the control. The LayoutTempate allows you to define the layout for everything else.
Let's say your wanted to render your data using a . your LayoutTemplate would contain your table definition with a single, empty row with ID "itemPlaceHolder"
<tr id="itemPlaceHolder" runat="server" />
Your item template would then define how your s should be rendered.