Django ORM window functions for analytics

                  from django.db.models import F, Window
from django.db.models.functions import RowNumber, Rank, DenseRank
from products.models import Sale


def get_sales_with_ranking():
    """Add rank to sales by amount."""
    sales = Sale.objects.annotate(
        rank=Window(
            expression=Rank(),
            order_by=F('amount').desc()
        ),
        row_number=Window(
            expression=RowNumber(),
            order_by=F('created_at').desc()
        )
    )
    return sales


def get_salesperson_rankings():
    """Rank salespeople within each region."""
    from django.db.models import Sum

    sales = Sale.objects.values(
        'salesperson__name',
        'salesperson__region'
    ).annotate(
        total_sales=Sum('amount')
    ).annotate(
        region_rank=Window(
            expression=Rank(),
            partition_by=[F('salesperson__region')],
            order_by=F('total_sales').desc()
        )
    ).order_by('salesperson__region', 'region_rank')

    return sales