django/tests/queries/test_qs_combinators.py

import operator

from django.db import DatabaseError, NotSupportedError, connection
from django.db.models import (
    Exists,
    F,
    IntegerField,
    OuterRef,
    Subquery,
    Transform,
    Value,
)
from django.db.models.functions import Mod
from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
from django.test.utils import CaptureQueriesContext

from .models import (
    Annotation,
    Author,
    Celebrity,
    ExtraInfo,
    Note,
    Number,
    ReservedName,
    Tag,
)


@skipUnlessDBFeature("supports_select_union")
class QuerySetSetOperationTests(TestCase):
    @classmethod
    def setUpTestData(cls):
        Number.objects.bulk_create(Number(num=i, other_num=10 - i) for i in range(10))

    def assertNumbersEqual(self, queryset, expected_numbers, ordered=True):
        self.assertQuerySetEqual(
            queryset, expected_numbers, operator.attrgetter("num"), ordered
        )

    def test_simple_union(self):
        qs1 = Number.objects.filter(num__lte=1)
        qs2 = Number.objects.filter(num__gte=8)
        qs3 = Number.objects.filter(num=5)
        self.assertNumbersEqual(qs1.union(qs2, qs3), [0, 1, 5, 8, 9], ordered=False)

    @skipUnlessDBFeature("supports_select_intersection")
    def test_simple_intersection(self):
        qs1 = Number.objects.filter(num__lte=5)
        qs2 = Number.objects.filter(num__gte=5)
        qs3 = Number.objects.filter(num__gte=4, num__lte=6)
        self.assertNumbersEqual(qs1.intersection(qs2, qs3), [5], ordered=False)

    @skipUnlessDBFeature("supports_select_intersection")
    def test_intersection_with_values(self):
        ReservedName.objects.create(name="a", order=2)
        qs1 = ReservedName.objects.all()
        reserved_name = qs1.intersection(qs1).values("name", "order", "id").get()
        self.assertEqual(reserved_name["name"], "a")
        self.assertEqual(reserved_name["order"], 2)
        reserved_name = qs1.intersection(qs1).values_list("name", "order", "id").get()
        self.assertEqual(reserved_name[:2], ("a", 2))

    @skipUnlessDBFeature("supports_select_difference")
    def test_simple_difference(self):
        qs1 = Number.objects.filter(num__lte=5)
        qs2 = Number.objects.filter(num__lte=4)
        self.assertNumbersEqual(qs1.difference(qs2), [5], ordered=False)

    def test_union_distinct(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.all()
        self.assertEqual(len(list(qs1.union(qs2, all=True))), 20)
        self.assertEqual(len(list(qs1.union(qs2))), 10)

    def test_union_none(self):
        qs1 = Number.objects.filter(num__lte=1)
        qs2 = Number.objects.filter(num__gte=8)
        qs3 = qs1.union(qs2)
        self.assertSequenceEqual(qs3.none(), [])
        self.assertNumbersEqual(qs3, [0, 1, 8, 9], ordered=False)

    def test_union_none_slice(self):
        qs1 = Number.objects.filter(num__lte=0)
        qs2 = Number.objects.none()
        qs3 = qs1.union(qs2)
        self.assertNumbersEqual(qs3[:1], [0])

    def test_union_all_none_slice(self):
        qs = Number.objects.filter(id__in=[])
        with self.assertNumQueries(0):
            self.assertSequenceEqual(qs.union(qs), [])
            self.assertSequenceEqual(qs.union(qs)[0:0], [])

    def test_union_empty_filter_slice(self):
        qs1 = Number.objects.filter(num__lte=0)
        qs2 = Number.objects.filter(pk__in=[])
        qs3 = qs1.union(qs2)
        self.assertNumbersEqual(qs3[:1], [0])

    @skipUnlessDBFeature("supports_slicing_ordering_in_compound")
    def test_union_slice_compound_empty(self):
        qs1 = Number.objects.filter(num__lte=0)[:1]
        qs2 = Number.objects.none()
        qs3 = qs1.union(qs2)
        self.assertNumbersEqual(qs3[:1], [0])

    @skipUnlessDBFeature("supports_slicing_ordering_in_compound")
    def test_union_combined_slice_compound_empty(self):
        qs1 = Number.objects.filter(num__lte=2)[:3]
        qs2 = Number.objects.none()
        qs3 = qs1.union(qs2)
        self.assertNumbersEqual(qs3.order_by("num")[2:3], [2])

    def test_union_slice_index(self):
        Celebrity.objects.create(name="Famous")
        c1 = Celebrity.objects.create(name="Very famous")

        qs1 = Celebrity.objects.filter(name="nonexistent")
        qs2 = Celebrity.objects.all()
        combined_qs = qs1.union(qs2).order_by("name")
        self.assertEqual(combined_qs[1], c1)

    def test_union_order_with_null_first_last(self):
        Number.objects.filter(other_num=5).update(other_num=None)
        qs1 = Number.objects.filter(num__lte=1)
        qs2 = Number.objects.filter(num__gte=2)
        qs3 = qs1.union(qs2)
        self.assertSequenceEqual(
            qs3.order_by(
                F("other_num").asc(nulls_first=True),
            ).values_list("other_num", flat=True),
            [None, 1, 2, 3, 4, 6, 7, 8, 9, 10],
        )
        self.assertSequenceEqual(
            qs3.order_by(
                F("other_num").asc(nulls_last=True),
            ).values_list("other_num", flat=True),
            [1, 2, 3, 4, 6, 7, 8, 9, 10, None],
        )

    def test_union_nested(self):
        qs1 = Number.objects.all()
        qs2 = qs1.union(qs1)
        self.assertNumbersEqual(
            qs1.union(qs2),
            [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
            ordered=False,
        )

    @skipUnlessDBFeature("supports_select_intersection")
    def test_intersection_with_empty_qs(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.none()
        qs3 = Number.objects.filter(pk__in=[])
        self.assertEqual(len(qs1.intersection(qs2)), 0)
        self.assertEqual(len(qs1.intersection(qs3)), 0)
        self.assertEqual(len(qs2.intersection(qs1)), 0)
        self.assertEqual(len(qs3.intersection(qs1)), 0)
        self.assertEqual(len(qs2.intersection(qs2)), 0)
        self.assertEqual(len(qs3.intersection(qs3)), 0)

    @skipUnlessDBFeature("supports_select_difference")
    def test_difference_with_empty_qs(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.none()
        qs3 = Number.objects.filter(pk__in=[])
        self.assertEqual(len(qs1.difference(qs2)), 10)
        self.assertEqual(len(qs1.difference(qs3)), 10)
        self.assertEqual(len(qs2.difference(qs1)), 0)
        self.assertEqual(len(qs3.difference(qs1)), 0)
        self.assertEqual(len(qs2.difference(qs2)), 0)
        self.assertEqual(len(qs3.difference(qs3)), 0)

    @skipUnlessDBFeature("supports_select_difference")
    def test_difference_with_values(self):
        ReservedName.objects.create(name="a", order=2)
        qs1 = ReservedName.objects.all()
        qs2 = ReservedName.objects.none()
        reserved_name = qs1.difference(qs2).values("name", "order", "id").get()
        self.assertEqual(reserved_name["name"], "a")
        self.assertEqual(reserved_name["order"], 2)
        reserved_name = qs1.difference(qs2).values_list("name", "order", "id").get()
        self.assertEqual(reserved_name[:2], ("a", 2))

    def test_union_with_empty_qs(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.none()
        qs3 = Number.objects.filter(pk__in=[])
        self.assertEqual(len(qs1.union(qs2)), 10)
        self.assertEqual(len(qs2.union(qs1)), 10)
        self.assertEqual(len(qs1.union(qs3)), 10)
        self.assertEqual(len(qs3.union(qs1)), 10)
        self.assertEqual(len(qs2.union(qs1, qs1, qs1)), 10)
        self.assertEqual(len(qs2.union(qs1, qs1, all=True)), 20)
        self.assertEqual(len(qs2.union(qs2)), 0)
        self.assertEqual(len(qs3.union(qs3)), 0)

    def test_empty_qs_union_with_ordered_qs(self):
        qs1 = Number.objects.order_by("num")
        qs2 = Number.objects.none().union(qs1).order_by("num")
        self.assertEqual(list(qs1), list(qs2))

    def test_limits(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.all()
        self.assertEqual(len(list(qs1.union(qs2)[:2])), 2)

    def test_ordering(self):
        qs1 = Number.objects.filter(num__lte=1)
        qs2 = Number.objects.filter(num__gte=2, num__lte=3)
        self.assertNumbersEqual(qs1.union(qs2).order_by("-num"), [3, 2, 1, 0])

    def test_ordering_by_alias(self):
        qs1 = Number.objects.filter(num__lte=1).values(alias=F("num"))
        qs2 = Number.objects.filter(num__gte=2, num__lte=3).values(alias=F("num"))
        self.assertQuerySetEqual(
            qs1.union(qs2).order_by("-alias"),
            [3, 2, 1, 0],
            operator.itemgetter("alias"),
        )

    def test_ordering_by_f_expression(self):
        qs1 = Number.objects.filter(num__lte=1)
        qs2 = Number.objects.filter(num__gte=2, num__lte=3)
        self.assertNumbersEqual(qs1.union(qs2).order_by(F("num").desc()), [3, 2, 1, 0])

    def test_ordering_by_f_expression_and_alias(self):
        qs1 = Number.objects.filter(num__lte=1).values(alias=F("other_num"))
        qs2 = Number.objects.filter(num__gte=2, num__lte=3).values(alias=F("other_num"))
        self.assertQuerySetEqual(
            qs1.union(qs2).order_by(F("alias").desc()),
            [10, 9, 8, 7],
            operator.itemgetter("alias"),
        )
        Number.objects.create(num=-1)
        self.assertQuerySetEqual(
            qs1.union(qs2).order_by(F("alias").desc(nulls_last=True)),
            [10, 9, 8, 7, None],
            operator.itemgetter("alias"),
        )

    def test_union_with_values(self):
        ReservedName.objects.create(name="a", order=2)
        qs1 = ReservedName.objects.all()
        reserved_name = qs1.union(qs1).values("name", "order", "id").get()
        self.assertEqual(reserved_name["name"], "a")
        self.assertEqual(reserved_name["order"], 2)
        reserved_name = qs1.union(qs1).values_list("name", "order", "id").get()
        self.assertEqual(reserved_name[:2], ("a", 2))
        # List of columns can be changed.
        reserved_name = qs1.union(qs1).values_list("order").get()
        self.assertEqual(reserved_name, (2,))

    def test_union_with_two_annotated_values_list(self):
        qs1 = (
            Number.objects.filter(num=1)
            .annotate(
                count=Value(0, IntegerField()),
            )
            .values_list("num", "count")
        )
        qs2 = (
            Number.objects.filter(num=2)
            .values("pk")
            .annotate(
                count=F("num"),
            )
            .annotate(
                num=Value(1, IntegerField()),
            )
            .values_list("num", "count")
        )
        self.assertCountEqual(qs1.union(qs2), [(1, 0), (1, 2)])

    def test_union_with_field_and_annotation_values(self):
        qs1 = (
            Number.objects.filter(num=1)
            .annotate(
                zero=Value(0, IntegerField()),
            )
            .values_list("num", "zero")
        )
        qs2 = (
            Number.objects.filter(num=2)
            .annotate(
                zero=Value(0, IntegerField()),
            )
            .values_list("zero", "num")
        )
        self.assertCountEqual(qs1.union(qs2), [(1, 0), (0, 2)])

    def test_union_with_extra_and_values_list(self):
        qs1 = (
            Number.objects.filter(num=1)
            .extra(
                select={"count": 0},
            )
            .values_list("num", "count")
        )
        qs2 = Number.objects.filter(num=2).extra(select={"count": 1})
        self.assertCountEqual(qs1.union(qs2), [(1, 0), (2, 1)])

    def test_union_with_values_list_on_annotated_and_unannotated(self):
        ReservedName.objects.create(name="rn1", order=1)
        qs1 = Number.objects.annotate(
            has_reserved_name=Exists(ReservedName.objects.filter(order=OuterRef("num")))
        ).filter(has_reserved_name=True)
        qs2 = Number.objects.filter(num=9)
        self.assertCountEqual(qs1.union(qs2).values_list("num", flat=True), [1, 9])

    def test_union_with_values_list_and_order(self):
        ReservedName.objects.bulk_create(
            [
                ReservedName(name="rn1", order=7),
                ReservedName(name="rn2", order=5),
                ReservedName(name="rn0", order=6),
                ReservedName(name="rn9", order=-1),
            ]
        )
        qs1 = ReservedName.objects.filter(order__gte=6)
        qs2 = ReservedName.objects.filter(order__lte=5)
        union_qs = qs1.union(qs2)
        for qs, expected_result in (
            # Order by a single column.
            (union_qs.order_by("-pk").values_list("order", flat=True), [-1, 6, 5, 7]),
            (union_qs.order_by("pk").values_list("order", flat=True), [7, 5, 6, -1]),
            (union_qs.values_list("order", flat=True).order_by("-pk"), [-1, 6, 5, 7]),
            (union_qs.values_list("order", flat=True).order_by("pk"), [7, 5, 6, -1]),
            # Order by multiple columns.
            (
                union_qs.order_by("-name", "pk").values_list("order", flat=True),
                [-1, 5, 7, 6],
            ),
            (
                union_qs.values_list("order", flat=True).order_by("-name", "pk"),
                [-1, 5, 7, 6],
            ),
        ):
            with self.subTest(qs=qs):
                self.assertEqual(list(qs), expected_result)

    def test_union_with_values_list_and_order_on_annotation(self):
        qs1 = Number.objects.annotate(
            annotation=Value(-1),
            multiplier=F("annotation"),
        ).filter(num__gte=6)
        qs2 = Number.objects.annotate(
            annotation=Value(2),
            multiplier=F("annotation"),
        ).filter(num__lte=5)
        self.assertSequenceEqual(
            qs1.union(qs2).order_by("annotation", "num").values_list("num", flat=True),
            [6, 7, 8, 9, 0, 1, 2, 3, 4, 5],
        )
        self.assertQuerySetEqual(
            qs1.union(qs2)
            .order_by(
                F("annotation") * F("multiplier"),
                "num",
            )
            .values("num"),
            [6, 7, 8, 9, 0, 1, 2, 3, 4, 5],
            operator.itemgetter("num"),
        )

    def test_order_by_annotation_transform(self):
        class Mod2(Mod, Transform):
            def __init__(self, expr):
                super().__init__(expr, 2)

        output_field = IntegerField()
        output_field.register_lookup(Mod2, "mod2")
        qs1 = Number.objects.annotate(
            annotation=Value(1, output_field=output_field),
        )
        qs2 = Number.objects.annotate(
            annotation=Value(2, output_field=output_field),
        )
        msg = "Ordering combined queries by transforms is not implemented."
        with self.assertRaisesMessage(NotImplementedError, msg):
            list(qs1.union(qs2).order_by("annotation__mod2"))

    def test_union_with_select_related_and_order(self):
        e1 = ExtraInfo.objects.create(value=7, info="e1")
        a1 = Author.objects.create(name="a1", num=1, extra=e1)
        a2 = Author.objects.create(name="a2", num=3, extra=e1)
        Author.objects.create(name="a3", num=2, extra=e1)
        base_qs = Author.objects.select_related("extra").order_by()
        qs1 = base_qs.filter(name="a1")
        qs2 = base_qs.filter(name="a2")
        self.assertSequenceEqual(qs1.union(qs2).order_by("pk"), [a1, a2])

    @skipUnlessDBFeature("supports_slicing_ordering_in_compound")
    def test_union_with_select_related_and_first(self):
        e1 = ExtraInfo.objects.create(value=7, info="e1")
        a1 = Author.objects.create(name="a1", num=1, extra=e1)
        Author.objects.create(name="a2", num=3, extra=e1)
        base_qs = Author.objects.select_related("extra").order_by()
        qs1 = base_qs.filter(name="a1")
        qs2 = base_qs.filter(name="a2")
        self.assertEqual(qs1.union(qs2).order_by("name").first(), a1)

    def test_union_with_first(self):
        e1 = ExtraInfo.objects.create(value=7, info="e1")
        a1 = Author.objects.create(name="a1", num=1, extra=e1)
        base_qs = Author.objects.order_by()
        qs1 = base_qs.filter(name="a1")
        qs2 = base_qs.filter(name="a2")
        self.assertEqual(qs1.union(qs2).first(), a1)

    def test_union_multiple_models_with_values_list_and_order(self):
        reserved_name = ReservedName.objects.create(name="rn1", order=0)
        qs1 = Celebrity.objects.all()
        qs2 = ReservedName.objects.all()
        self.assertSequenceEqual(
            qs1.union(qs2).order_by("name").values_list("pk", flat=True),
            [reserved_name.pk],
        )

    def test_union_multiple_models_with_values_list_and_order_by_extra_select(self):
        reserved_name = ReservedName.objects.create(name="rn1", order=0)
        qs1 = Celebrity.objects.extra(select={"extra_name": "name"})
        qs2 = ReservedName.objects.extra(select={"extra_name": "name"})
        self.assertSequenceEqual(
            qs1.union(qs2).order_by("extra_name").values_list("pk", flat=True),
            [reserved_name.pk],
        )

    def test_union_multiple_models_with_values_list_and_annotations(self):
        ReservedName.objects.create(name="rn1", order=10)
        Celebrity.objects.create(name="c1")
        qs1 = ReservedName.objects.annotate(row_type=Value("rn")).values_list(
            "name", "order", "row_type"
        )
        qs2 = Celebrity.objects.annotate(
            row_type=Value("cb"), order=Value(-10)
        ).values_list("name", "order", "row_type")
        self.assertSequenceEqual(
            qs1.union(qs2).order_by("order"),
            [("c1", -10, "cb"), ("rn1", 10, "rn")],
        )

    def test_union_in_subquery(self):
        ReservedName.objects.bulk_create(
            [
                ReservedName(name="rn1", order=8),
                ReservedName(name="rn2", order=1),
                ReservedName(name="rn3", order=5),
            ]
        )
        qs1 = Number.objects.filter(num__gt=7, num=OuterRef("order"))
        qs2 = Number.objects.filter(num__lt=2, num=OuterRef("order"))
        self.assertCountEqual(
            ReservedName.objects.annotate(
                number=Subquery(qs1.union(qs2).values("num")),
            )
            .filter(number__isnull=False)
            .values_list("order", flat=True),
            [8, 1],
        )

    @skipUnlessDBFeature("supports_select_intersection")
    def test_intersection_in_nested_subquery(self):
        tag = Tag.objects.create(name="tag")
        note = Note.objects.create(tag=tag)
        annotation = Annotation.objects.create(tag=tag)
        tags = Tag.objects.order_by()
        tags = tags.filter(id=OuterRef("tag_id")).intersection(
            tags.filter(id=OuterRef(OuterRef("tag_id")))
        )
        qs = Note.objects.filter(
            Exists(
                Annotation.objects.filter(
                    Exists(tags),
                    notes__in=OuterRef("pk"),
                )
            )
        )
        self.assertIsNone(qs.first())
        annotation.notes.add(note)
        self.assertEqual(qs.first(), note)

    def test_union_in_subquery_related_outerref(self):
        e1 = ExtraInfo.objects.create(value=7, info="e3")
        e2 = ExtraInfo.objects.create(value=5, info="e2")
        e3 = ExtraInfo.objects.create(value=1, info="e1")
        Author.objects.bulk_create(
            [
                Author(name="a1", num=1, extra=e1),
                Author(name="a2", num=3, extra=e2),
                Author(name="a3", num=2, extra=e3),
            ]
        )
        qs1 = ExtraInfo.objects.order_by().filter(value=OuterRef("num"))
        qs2 = ExtraInfo.objects.order_by().filter(value__lt=OuterRef("extra__value"))
        qs = (
            Author.objects.annotate(
                info=Subquery(qs1.union(qs2).values("info")[:1]),
            )
            .filter(info__isnull=False)
            .values_list("name", flat=True)
        )
        self.assertCountEqual(qs, ["a1", "a2"])
        # Combined queries don't mutate.
        self.assertCountEqual(qs, ["a1", "a2"])

    @skipUnlessDBFeature("supports_slicing_ordering_in_compound")
    def test_union_in_with_ordering(self):
        qs1 = Number.objects.filter(num__gt=7).order_by("num")
        qs2 = Number.objects.filter(num__lt=2).order_by("num")
        self.assertNumbersEqual(
            Number.objects.exclude(id__in=qs1.union(qs2).values("id")),
            [2, 3, 4, 5, 6, 7],
            ordered=False,
        )

    @skipUnlessDBFeature(
        "supports_slicing_ordering_in_compound", "allow_sliced_subqueries_with_in"
    )
    def test_union_in_with_ordering_and_slice(self):
        qs1 = Number.objects.filter(num__gt=7).order_by("num")[:1]
        qs2 = Number.objects.filter(num__lt=2).order_by("-num")[:1]
        self.assertNumbersEqual(
            Number.objects.exclude(id__in=qs1.union(qs2).values("id")),
            [0, 2, 3, 4, 5, 6, 7, 9],
            ordered=False,
        )

    def test_count_union(self):
        qs1 = Number.objects.filter(num__lte=1).values("num")
        qs2 = Number.objects.filter(num__gte=2, num__lte=3).values("num")
        self.assertEqual(qs1.union(qs2).count(), 4)

    def test_count_union_empty_result(self):
        qs = Number.objects.filter(pk__in=[])
        self.assertEqual(qs.union(qs).count(), 0)

    def test_count_union_with_select_related(self):
        e1 = ExtraInfo.objects.create(value=1, info="e1")
        Author.objects.create(name="a1", num=1, extra=e1)
        qs = Author.objects.select_related("extra").order_by()
        self.assertEqual(qs.union(qs).count(), 1)

    @skipUnlessDBFeature("supports_select_difference")
    def test_count_difference(self):
        qs1 = Number.objects.filter(num__lt=10)
        qs2 = Number.objects.filter(num__lt=9)
        self.assertEqual(qs1.difference(qs2).count(), 1)

    @skipUnlessDBFeature("supports_select_intersection")
    def test_count_intersection(self):
        qs1 = Number.objects.filter(num__gte=5)
        qs2 = Number.objects.filter(num__lte=5)
        self.assertEqual(qs1.intersection(qs2).count(), 1)

    def test_exists_union(self):
        qs1 = Number.objects.filter(num__gte=5)
        qs2 = Number.objects.filter(num__lte=5)
        with CaptureQueriesContext(connection) as context:
            self.assertIs(qs1.union(qs2).exists(), True)
        captured_queries = context.captured_queries
        self.assertEqual(len(captured_queries), 1)
        captured_sql = captured_queries[0]["sql"]
        self.assertNotIn(
            connection.ops.quote_name(Number._meta.pk.column),
            captured_sql,
        )
        self.assertEqual(
            captured_sql.count(connection.ops.limit_offset_sql(None, 1)), 1
        )

    def test_exists_union_empty_result(self):
        qs = Number.objects.filter(pk__in=[])
        self.assertIs(qs.union(qs).exists(), False)

    @skipUnlessDBFeature("supports_select_intersection")
    def test_exists_intersection(self):
        qs1 = Number.objects.filter(num__gt=5)
        qs2 = Number.objects.filter(num__lt=5)
        self.assertIs(qs1.intersection(qs1).exists(), True)
        self.assertIs(qs1.intersection(qs2).exists(), False)

    @skipUnlessDBFeature("supports_select_difference")
    def test_exists_difference(self):
        qs1 = Number.objects.filter(num__gte=5)
        qs2 = Number.objects.filter(num__gte=3)
        self.assertIs(qs1.difference(qs2).exists(), False)
        self.assertIs(qs2.difference(qs1).exists(), True)

    def test_get_union(self):
        qs = Number.objects.filter(num=2)
        self.assertEqual(qs.union(qs).get().num, 2)

    @skipUnlessDBFeature("supports_select_difference")
    def test_get_difference(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.exclude(num=2)
        self.assertEqual(qs1.difference(qs2).get().num, 2)

    @skipUnlessDBFeature("supports_select_intersection")
    def test_get_intersection(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.filter(num=2)
        self.assertEqual(qs1.intersection(qs2).get().num, 2)

    @skipUnlessDBFeature("supports_slicing_ordering_in_compound")
    def test_ordering_subqueries(self):
        qs1 = Number.objects.order_by("num")[:2]
        qs2 = Number.objects.order_by("-num")[:2]
        self.assertNumbersEqual(qs1.union(qs2).order_by("-num")[:4], [9, 8, 1, 0])

    @skipIfDBFeature("supports_slicing_ordering_in_compound")
    def test_unsupported_ordering_slicing_raises_db_error(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.all()
        qs3 = Number.objects.all()
        msg = "LIMIT/OFFSET not allowed in subqueries of compound statements"
        with self.assertRaisesMessage(DatabaseError, msg):
            list(qs1.union(qs2[:10]))
        msg = "ORDER BY not allowed in subqueries of compound statements"
        with self.assertRaisesMessage(DatabaseError, msg):
            list(qs1.order_by("id").union(qs2))
        with self.assertRaisesMessage(DatabaseError, msg):
            list(qs1.union(qs2).order_by("id").union(qs3))

    @skipIfDBFeature("supports_select_intersection")
    def test_unsupported_intersection_raises_db_error(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.all()
        msg = "intersection is not supported on this database backend"
        with self.assertRaisesMessage(NotSupportedError, msg):
            list(qs1.intersection(qs2))

    def test_combining_multiple_models(self):
        ReservedName.objects.create(name="99 little bugs", order=99)
        qs1 = Number.objects.filter(num=1).values_list("num", flat=True)
        qs2 = ReservedName.objects.values_list("order")
        self.assertEqual(list(qs1.union(qs2).order_by("num")), [1, 99])

    def test_order_raises_on_non_selected_column(self):
        qs1 = (
            Number.objects.filter()
            .annotate(
                annotation=Value(1, IntegerField()),
            )
            .values("annotation", num2=F("num"))
        )
        qs2 = Number.objects.filter().values("id", "num")
        # Should not raise
        list(qs1.union(qs2).order_by("annotation"))
        list(qs1.union(qs2).order_by("num2"))
        msg = "ORDER BY term does not match any column in the result set"
        # 'id' is not part of the select
        with self.assertRaisesMessage(DatabaseError, msg):
            list(qs1.union(qs2).order_by("id"))
        # 'num' got realiased to num2
        with self.assertRaisesMessage(DatabaseError, msg):
            list(qs1.union(qs2).order_by("num"))
        with self.assertRaisesMessage(DatabaseError, msg):
            list(qs1.union(qs2).order_by(F("num")))
        with self.assertRaisesMessage(DatabaseError, msg):
            list(qs1.union(qs2).order_by(F("num").desc()))
        # switched order, now 'exists' again:
        list(qs2.union(qs1).order_by("num"))

    @skipUnlessDBFeature("supports_select_difference", "supports_select_intersection")
    def test_qs_with_subcompound_qs(self):
        qs1 = Number.objects.all()
        qs2 = Number.objects.intersection(Number.objects.filter(num__gt=1))
        self.assertEqual(qs1.difference(qs2).count(), 2)

    def test_order_by_same_type(self):
        qs = Number.objects.all()
        union = qs.union(qs)
        numbers = list(range(10))
        self.assertNumbersEqual(union.order_by("num"), numbers)
        self.assertNumbersEqual(union.order_by("other_num"), reversed(numbers))

    def test_unsupported_operations_on_combined_qs(self):
        qs = Number.objects.all()
        msg = "Calling QuerySet.%s() after %s() is not supported."
        combinators = ["union"]
        if connection.features.supports_select_difference:
            combinators.append("difference")
        if connection.features.supports_select_intersection:
            combinators.append("intersection")
        for combinator in combinators:
            for operation in (
                "alias",
                "annotate",
                "defer",
                "delete",
                "distinct",
                "exclude",
                "extra",
                "filter",
                "only",
                "prefetch_related",
                "select_related",
                "update",
            ):
                with self.subTest(combinator=combinator, operation=operation):
                    with self.assertRaisesMessage(
                        NotSupportedError,
                        msg % (operation, combinator),
                    ):
                        getattr(getattr(qs, combinator)(qs), operation)()
            with self.assertRaisesMessage(
                NotSupportedError,
                msg % ("contains", combinator),
            ):
                obj = Number.objects.first()
                getattr(qs, combinator)(qs).contains(obj)

    def test_get_with_filters_unsupported_on_combined_qs(self):
        qs = Number.objects.all()
        msg = "Calling QuerySet.get(...) with filters after %s() is not supported."
        combinators = ["union"]
        if connection.features.supports_select_difference:
            combinators.append("difference")
        if connection.features.supports_select_intersection:
            combinators.append("intersection")
        for combinator in combinators:
            with self.subTest(combinator=combinator):
                with self.assertRaisesMessage(NotSupportedError, msg % combinator):
                    getattr(qs, combinator)(qs).get(num=2)

    def test_operator_on_combined_qs_error(self):
        qs = Number.objects.all()
        msg = "Cannot use %s operator with combined queryset."
        combinators = ["union"]
        if connection.features.supports_select_difference:
            combinators.append("difference")
        if connection.features.supports_select_intersection:
            combinators.append("intersection")
        operators = [
            ("|", operator.or_),
            ("&", operator.and_),
            ("^", operator.xor),
        ]
        for combinator in combinators:
            combined_qs = getattr(qs, combinator)(qs)
            for operator_, operator_func in operators:
                with self.subTest(combinator=combinator):
                    with self.assertRaisesMessage(TypeError, msg % operator_):
                        operator_func(qs, combined_qs)
                    with self.assertRaisesMessage(TypeError, msg % operator_):
                        operator_func(combined_qs, qs)