making_queries_q1.py

from django.db.models import Case, IntegerField, Sum, Value, When
from django.db.models.functions import Coalesce

q = Exam.objects.aggregate(
    success=Coalesce(
        Sum(
            Case(
                When(score__gte=85, then=Value(1)),
                default=Value(0),
                output_field=IntegerField(),
            )
        ),
        Value(0),
    ),
)

print(q)
# {"success": 5}