To receive by one request a difference of two last values ​​in selection?

Question

Django

A selection is made

res = SomeModel.objects.filter(user=someuser).order_by('somedate').values_list('somevalue', flat=True)

The result of which will be an array of values.
How can I get the difference of the last two values ​​in one query? Considering that there can be less than two values ​​(then display 0)
Something like res[-1] - res[-2] - only at the level of database queries

Answer 1

two cursors at the DB level. All this should be done in the form of a stored procedure.
I don't know any other option