What is the most complex database query you have had to implement in Django?

In Django, the most complex query is often one that requires joining multiple tables with filtering, aggregation, and annotations.

For example, a query to get a list of users with the number of their active orders in the last month, where orders are grouped by status and sorted by quantity:

from django.db.models import Count, Q
from django.utils.timezone import now
from datetime import timedelta

one_month_ago = now() - timedelta(days=30)

users = User.objects.annotate(
    active_orders_count=Count('orders', filter=Q(orders__status='active', orders__created_at__gte=one_month_ago))
).filter(active_orders_count__gt=0).order_by('-active_orders_count')

Such a query combines:

• Filtering related objects (orders__status='active')
• Using annotations and aggregate functions (Count)
• Filtering by date
• Sorting by a computed field

In more complex cases, it is necessary to use Subquery, Prefetch, or even RawSQL for optimization and implementation of specific queries.