>Actually, I think that is a good question.
>I'm trying to create a relationship between two tables through record ids, but I want the child table to be in reverse date order.
>
>Do you think I going about it correctly?

In your current task description you're correct. If, for example, you would want a key based on a numeric field (not integer) in ascending order
and a date in descending order, you would use something like:

padl(myNumField,10,'0') + padl({^9999-01-01} - DateField),10,'0')

The idea was discussed long time ago here as well.

But it would not work for NULL and empty dates, so the index expression should be a little bit more complex...