diff --git a/accountant/models/operations.py b/accountant/models/operations.py
index 5489698..0608bbf 100644
--- a/accountant/models/operations.py
+++ b/accountant/models/operations.py
@@ -134,22 +134,33 @@ class Operation(db.Model):
         return query
 
     @classmethod
-    def get_categories_for_range(cls, account, begin, end):
-        """Get category list for a specific time period."""
+    def query_category_incomes(cls, account, begin=None, end=None):
+        """Return a query for categories with expenses, revenues and income for
+        a specific account and a specific time period."""
         if isinstance(account, (int, str)):
             account_id = account
         else:
             account_id = account.id
 
         query = db.session.query(
-            cls.category,
-            db.func.sum(
-                db.case([(db.func.sign(cls.value) == -1, cls.value)], else_=0)
+            cls.category.label('category'),
+            db.func.coalesce(
+                db.func.sum(
+                    cls.value
+                ).filter(
+                    db.func.sign(cls.value) == -1
+                ),
+                0
             ).label("expenses"),
-            db.func.sum(
-                db.case([(db.func.sign(cls.value) == 1, cls.value)], else_=0)
+            db.func.coalesce(
+                db.func.sum(
+                    cls.value
+                ).filter(
+                    db.func.sign(cls.value) == 1
+                ),
+                0
             ).label("revenues"),
-            db.func.sum(cls.value).label("balance")
+            db.func.sum(cls.value).label("income")
         ).filter(
             cls.account_id == account_id
         ).order_by(
diff --git a/accountant/views/accounts.py b/accountant/views/accounts.py
index 093e3df..2719fe9 100644
--- a/accountant/views/accounts.py
+++ b/accountant/views/accounts.py
@@ -326,8 +326,11 @@ class CategoryResource(Resource):
         """Get account category balances for a specific date range."""
 
         data = range_parser.parse_args()
+        # FIXME Alexis Lahouze 2017-05-23 check data.
 
-        return Operation.get_categories_for_range(account_id, **data).all()
+        return list(result_as_dicts(
+            Operation.query_category_incomes(account_id, **data)
+        )), 200
 
 
 @ns.route('/<int:account_id>/daily_balances')