SPQuery OrderBy is not working on custom Number field

Question

I have one custom column named 'fhdr_Index' which is type of Number field.

I want to get maximum number in this column so i have applied Order By with Ascending 'FALSE' and RowLimit =1 . But query is not working.

                    qry.Query =
                    @"   <Where>
                            <IsNotNull>
                               <FieldRef Name='ID'/>
                            </IsNotNull>
                        </Where>
                           <OrderBy >
                              <FieldRef  Name='fhdr_Index' Ascending='FALSE' />
                           </OrderBy>";
                    qry.RowLimit = 1;
                    SPListItemCollection listItems = spList.GetItems(qry);

First item from list is return. And If i apply query on ID column rather then fhdr_Index column query is working. 

Answer 1

Make sure you have enabled indexing attribute to true for the custom field in the schema.

<Field ID="{59956c56-30dd-4cb1-bf12-ef693b42679c}" Name="fhdr_Index" ... Indexed="TRUE">

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