diff --git a/sqlalchemy_utils/aggregates.py b/sqlalchemy_utils/aggregates.py
index 69e1087..a5f8caf 100644
--- a/sqlalchemy_utils/aggregates.py
+++ b/sqlalchemy_utils/aggregates.py
@@ -374,7 +374,7 @@ from .functions.orm import get_column_key
 from .relationships import (
     chained_join,
     path_to_relationships,
-    select_aggregate
+    select_correlated_expression
 )
 
 
@@ -447,9 +447,14 @@ class AggregatedValue(object):
 
     @property
     def aggregate_query(self):
-        query = select_aggregate(self.expr, self.relationships)
+        query = select_correlated_expression(
+            self.class_,
+            self.expr,
+            self.path,
+            self.relationships[0].mapper.class_
+        )
 
-        return query.correlate(self.class_).as_scalar()
+        return query.as_scalar()
 
     def update_query(self, objects):
         table = self.class_.__table__
diff --git a/sqlalchemy_utils/listeners.py b/sqlalchemy_utils/listeners.py
index ce6d774..691578b 100644
--- a/sqlalchemy_utils/listeners.py
+++ b/sqlalchemy_utils/listeners.py
@@ -23,7 +23,7 @@ def coercion_listener(mapper, class_):
 
 def instant_defaults_listener(target, args, kwargs):
     for key, column in sa.inspect(target.__class__).columns.items():
-        if column.default is not None:
+        if hasattr(column, 'default') and column.default is not None:
             if callable(column.default.arg):
                 setattr(target, key, column.default.arg(target))
             else:
diff --git a/sqlalchemy_utils/relationships/__init__.py b/sqlalchemy_utils/relationships/__init__.py
index 8069c65..1bbb85d 100644
--- a/sqlalchemy_utils/relationships/__init__.py
+++ b/sqlalchemy_utils/relationships/__init__.py
@@ -2,7 +2,6 @@ import sqlalchemy as sa
 from sqlalchemy.sql.util import ClauseAdapter
 
 from .chained_join import chained_join  # noqa
-from .select_aggregate import select_aggregate  # noqa
 
 
 def path_to_relationships(path, cls):
diff --git a/sqlalchemy_utils/relationships/select_aggregate.py b/sqlalchemy_utils/relationships/select_aggregate.py
deleted file mode 100644
index 379b33f..0000000
--- a/sqlalchemy_utils/relationships/select_aggregate.py
+++ /dev/null
@@ -1,51 +0,0 @@
-import sqlalchemy as sa
-
-
-def select_aggregate(agg_expr, relationships):
-    """
-    Return a subquery for fetching an aggregate value of given aggregate
-    expression and given sequence of relationships.
-
-    The returned aggregate query can be used when updating denormalized column
-    value with query such as:
-
-    UPDATE table SET column = {aggregate_query}
-    WHERE {condition}
-
-    :param agg_expr:
-        an expression to be selected, for example sa.func.count('1')
-    :param relationships:
-        Sequence of relationships to be used for building the aggregate
-        query.
-    """
-    from_ = relationships[0].mapper.class_.__table__
-    for relationship in relationships[0:-1]:
-        property_ = relationship.property
-        if property_.secondary is not None:
-            from_ = from_.join(
-                property_.secondary,
-                property_.secondaryjoin
-            )
-
-        from_ = (
-            from_
-            .join(
-                property_.parent.class_,
-                property_.primaryjoin
-            )
-        )
-
-    prop = relationships[-1].property
-    condition = prop.primaryjoin
-    if prop.secondary is not None:
-        from_ = from_.join(
-            prop.secondary,
-            prop.secondaryjoin
-        )
-
-    query = sa.select(
-        [agg_expr],
-        from_obj=[from_]
-    )
-
-    return query.where(condition)
diff --git a/tests/relationships/test_select_aggregate.py b/tests/relationships/test_select_aggregate.py
deleted file mode 100644
index f4fe687..0000000
--- a/tests/relationships/test_select_aggregate.py
+++ /dev/null
@@ -1,61 +0,0 @@
-import sqlalchemy as sa
-
-from sqlalchemy_utils.aggregates import select_aggregate
-from tests import TestCase
-from tests.mixins import ThreeLevelDeepManyToMany
-
-
-def normalize(sql):
-    return ' '.join(sql.replace('\n', '').split())
-
-
-class TestAggregateQueryForDeepToManyToMany(
-    ThreeLevelDeepManyToMany,
-    TestCase
-):
-    dns = 'postgres://postgres@localhost/sqlalchemy_utils_test'
-    create_tables = False
-
-    def assert_sql(self, construct, sql):
-        assert normalize(str(construct)) == normalize(sql)
-
-    def build_update(self, *relationships):
-        expr = sa.func.count(sa.text('1'))
-        return (
-            self.Catalog.__table__.update().values(
-                _id=select_aggregate(
-                    expr,
-                    relationships
-                ).correlate(self.Catalog)
-            )
-        )
-
-    def test_simple_join(self):
-        self.assert_sql(
-            self.build_update(self.Catalog.categories),
-            (
-                '''UPDATE catalog SET _id=(SELECT count(1) AS count_1
-                FROM category JOIN catalog_category ON category._id =
-                catalog_category.category_id WHERE catalog._id =
-                catalog_category.catalog_id)'''
-            )
-        )
-
-    def test_two_relations(self):
-        self.assert_sql(
-            self.build_update(
-                self.Category.sub_categories,
-                self.Catalog.categories,
-            ),
-            (
-                '''UPDATE catalog SET _id=(SELECT count(1) AS count_1
-                FROM sub_category
-                JOIN category_subcategory
-                    ON sub_category._id = category_subcategory.subcategory_id
-                JOIN category
-                    ON category._id = category_subcategory.category_id
-                JOIN catalog_category
-                    ON category._id = catalog_category.category_id
-                WHERE catalog._id = catalog_category.catalog_id)'''
-            )
-        )