Sorting a table by it's object value

Hi guys!

I have a database that contain an "historic value" object, that contains 2 fields
- date
- value

Everyday I run a job to add a new record in that object to save it's historic value.

I use it to save daily user statistic data.

Now I would like to be able to sort my main table by the values inside that object.

The goal is to sort users with the highest object value sum on top and lowest at the bottom.

I'm not sure if this is possible using the External Sorting method, as it will require some mathematical equation inside the object.

Any ideas how this can be done?