Can I order by Content Type in a CAML query?

Question

Is it possible to order by content type in a CAML query?

I seem to always get the same result no matter what I do with the Order by. Ordering by ID instead works perfectly.

query.Query = @"
    <Where>
        <And>
            <BeginsWith>
                <FieldRef Name='ContentTypeId' />
                <Value Type='ContentTypeId'>0x010039EFCF9C11783C409E74551800AB7525</Value>
            </BeginsWith>
            <Eq>
                <FieldRef Name='SectionTitle' />
                <Value Type='Lookup'>" + filter + @"</Value>
            </Eq>
        </And>
    </Where>
    <OrderBy Override='TRUE'>
        <FieldRef Name='ContentType' Ascending='FALSE' />
    </OrderBy>";

Answer 1

That looks like it should work. I know it's not optimal but, as an alternative, you could do the sorting on the client side.

var items = list.GetItems(query).OfType<SPListItem>().OrderByDescending(i => i["ContentType"]);

Answer 2

My understanding is that the schema of the list and fields defines whether or not a field is sortable. For ContentType field "Sortable" (that's a boolean attribute) must have been set to False.

That's the reason it is not available when you create view for your list; the field is not available in the dropdown. Same restrictions would apply to SPQuery also.