>>>How do you write an index expression where the first field needs to be descending, but the second may need to be ascending?
>>What type is the first field?
>
>Logical, then the 2nd is character.

If you need to make the second field in descending order, then there was a great solution by Fabio L, I can search. But it is much easier to just use set order in select statement.

Do you really need this as an index?