diff options
| -rw-r--r-- | django/db/models/sql/compiler.py | 72 | ||||
| -rw-r--r-- | tests/queries/test_qs_combinators.py | 6 |
2 files changed, 44 insertions, 34 deletions
diff --git a/django/db/models/sql/compiler.py b/django/db/models/sql/compiler.py index 98feb42716..262d722dc1 100644 --- a/django/db/models/sql/compiler.py +++ b/django/db/models/sql/compiler.py @@ -583,50 +583,28 @@ class SQLCompiler: raise DatabaseError( "ORDER BY not allowed in subqueries of compound statements." ) - elif self.query.is_sliced and combinator == "union": - for compiler in compilers: - # A sliced union cannot have its parts elided as some of them - # might be sliced as well and in the event where only a single - # part produces a non-empty resultset it might be impossible to - # generate valid SQL. - compiler.elide_empty = False - parts = () - selected = self.query.selected + parts = [] + empty_compiler = None for compiler in compilers: try: - # If the columns list is limited, then all combined queries - # must have the same columns list. Set the selects defined on - # the query on all combined queries, if not already set. - if selected is not None and compiler.query.selected is None: - compiler.query = compiler.query.clone() - compiler.query.set_values(selected) - part_sql, part_args = compiler.as_sql(with_col_aliases=True) - if compiler.query.combinator: - # Wrap in a subquery if wrapping in parentheses isn't - # supported. - if not features.supports_parentheses_in_compound: - part_sql = "SELECT * FROM ({})".format(part_sql) - # Add parentheses when combining with compound query if not - # already added for all compound queries. - elif ( - self.query.subquery - or not features.supports_slicing_ordering_in_compound - ): - part_sql = "({})".format(part_sql) - elif ( - self.query.subquery - and features.supports_slicing_ordering_in_compound - ): - part_sql = "({})".format(part_sql) - parts += ((part_sql, part_args),) + parts.append(self._get_combinator_part_sql(compiler)) except EmptyResultSet: # Omit the empty queryset with UNION and with DIFFERENCE if the # first queryset is nonempty. if combinator == "union" or (combinator == "difference" and parts): + empty_compiler = compiler continue raise if not parts: raise EmptyResultSet + elif len(parts) == 1 and combinator == "union" and self.query.is_sliced: + # A sliced union cannot be composed of a single component because + # in the event the later is also sliced it might result in invalid + # SQL due to the usage of multiple LIMIT clauses. Prevent that from + # happening by always including an empty resultset query to force + # the creation of an union. + empty_compiler.elide_empty = False + parts.append(self._get_combinator_part_sql(empty_compiler)) combinator_sql = self.connection.ops.set_operators[combinator] if all and combinator == "union": combinator_sql += " ALL" @@ -642,6 +620,32 @@ class SQLCompiler: params.extend(part) return result, params + def _get_combinator_part_sql(self, compiler): + features = self.connection.features + # If the columns list is limited, then all combined queries + # must have the same columns list. Set the selects defined on + # the query on all combined queries, if not already set. + selected = self.query.selected + if selected is not None and compiler.query.selected is None: + compiler.query = compiler.query.clone() + compiler.query.set_values(selected) + part_sql, part_args = compiler.as_sql(with_col_aliases=True) + if compiler.query.combinator: + # Wrap in a subquery if wrapping in parentheses isn't + # supported. + if not features.supports_parentheses_in_compound: + part_sql = "SELECT * FROM ({})".format(part_sql) + # Add parentheses when combining with compound query if not + # already added for all compound queries. + elif ( + self.query.subquery + or not features.supports_slicing_ordering_in_compound + ): + part_sql = "({})".format(part_sql) + elif self.query.subquery and features.supports_slicing_ordering_in_compound: + part_sql = "({})".format(part_sql) + return part_sql, part_args + def get_qualify_sql(self): where_parts = [] if self.where: diff --git a/tests/queries/test_qs_combinators.py b/tests/queries/test_qs_combinators.py index eac1533803..ad1017c8af 100644 --- a/tests/queries/test_qs_combinators.py +++ b/tests/queries/test_qs_combinators.py @@ -76,6 +76,12 @@ class QuerySetSetOperationTests(TestCase): 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=[]) |