Circumventing (legacy) Django's need to add `extra`'s `select`s to GROUP BY.

gistfile1.py

# -*- coding: utf-8 -*-

# TODO FIXME HARD-CODING KLUDGE MONKEYS PATCHING EACH OTHER
# Django (1.2 at least), I DON'T LIKE YOU
class FakeSQLUnicode(unicode):
    def as_sql(*args, **kwargs):
        # See django.db.models.sql.compiler, get_grouping, the place with `hasattr(col, 'as_sql')
        # MySQL GROUP BY doesn't work with COALESCE() in GROUP BY,
        # failing with Database error 1111, "invalid use of group function".
        # Solution: convert the aggregate to the `id` which is there anyway! :D
        return '`store_product`.`id`'
    

extra_select = FakeSQLUnicode('''
    COALESCE(
        MIN(`store_variation`.`discount_price`), 
        MIN(`store_variation`.`price`)
    )''')

additional_select = 'lowest_available_price'
products = products.annotate(
    # Unused annotation to skip manual joins
    min_normal_price=Min('variations__price'),
    ).extra(select={'lowest_available_price': extra_select}).order_by(
        'lowest_available_price'
    )