orderby disabled where not needed

gluon/dal.py

@@ -9833,7 +9833,7 @@ class Set(object):
         return built
 
     def isempty(self):
-        return not self.select(limitby=(0,1))
+        return not self.select(limitby=(0,1), orderby_on_limitby=False)
 
     def count(self,distinct=None, cache=None):
         db = self.db

gluon/tests/test_dal.py

@@ -236,9 +236,12 @@ class TestInsert(unittest.TestCase):
         self.assertEqual(db.tt.insert(aa='1'), 2)
         self.assertEqual(db.tt.insert(aa='1'), 3)
         self.assertEqual(db(db.tt.aa == '1').count(), 3)
+        self.assertEqual(db(db.tt.aa == '2').isempty(), True)
         self.assertEqual(db(db.tt.aa == '1').update(aa='2'), 3)
         self.assertEqual(db(db.tt.aa == '2').count(), 3)
+        self.assertEqual(db(db.tt.aa == '2').isempty(), False)
         self.assertEqual(db(db.tt.aa == '2').delete(), 3)
+        self.assertEqual(db(db.tt.aa == '2').isempty(), True)
         db.tt.drop()
 
 

gluon/validators.py

@@ -648,11 +648,11 @@ class IS_NOT_IN_DB(Validator):
         id = self.record_id
         if isinstance(id, dict):
             fields = [table[f] for f in id]
-            row = subset.select(*fields, **dict(limitby=(0, 1))).first()
+            row = subset.select(*fields, **dict(limitby=(0, 1), orderby_on_limitby=False)).first()
             if row and any(str(row[f]) != str(id[f]) for f in id):
                 return (value, translate(self.error_message))
         else:
-            row = subset.select(table._id, field, limitby=(0, 1)).first()
+            row = subset.select(table._id, field, limitby=(0, 1), orderby_on_limitby=False).first()
             if row and str(row.id) != str(id):
                 return (value, translate(self.error_message))
         return (value, None)