> A constraint or an index?

It's not a matter, I can create as need.
I think will be index because I need descending...

> Indices can be ASCending or DESCending, constraints create indices
> which are ASCending.

> Create an addition DESCending index and you should be home free.

Two index? ASCending and DESCending? ok, I will try

> Generate some test data and test it's behaviour yourself.

I no need generate more, I have loads of date, but trying never can
see they use great optimized, for only 3 years, always reading
thousands of record to look for MAX ...

In the case I exposed, what is the recomanded Indexes or Constraints?