: Not sure how you are indexing, but in addition to the above : suggestion by Yonik, one could ignore 0's at indexing time, : i.e., ensure that 0 values for that field are not indexed, and : use sortMissingLast.
Once upon a time i had a usecase where i was indexing product data, and in thta product data a null price ment not currently for sale, but "0" was a legal price for products that were being given away free. i had a similar requirement that the default sort should be based on price, but "free" products should come last ... except if the user explicitly said "sort by price". what i did was to index a "hasPrice" field that was true if the price field existed and was non-zero. my default sort was "hasPrice desc, price asc" but if the user clicked "sort by price" it was "price asc" that might give you ideas about your own usecase. -Hoss
