diff --git a/include/sqlpp11/assignment.h b/include/sqlpp11/assignment.h
index 5fc5872d..929523e1 100644
--- a/include/sqlpp11/assignment.h
+++ b/include/sqlpp11/assignment.h
@@ -41,7 +41,8 @@ namespace sqlpp
     using _rhs_t = Rhs;
     using _nodes = detail::type_vector<_lhs_t, _rhs_t>;
 
-    static_assert(can_be_null_t<_lhs_t>::value ? true
+#warning: We check this in the factory function
+    static_assert(can_be_null<_lhs_t>::value ? true
                                                : not std::is_same<_rhs_t, null_t>::value,
                   "column must not be null");
 
diff --git a/include/sqlpp11/column.h b/include/sqlpp11/column.h
index 547c342c..e9158300 100644
--- a/include/sqlpp11/column.h
+++ b/include/sqlpp11/column.h
@@ -47,13 +47,11 @@ namespace sqlpp
     struct _traits
     {
       using _value_type = typename ColumnSpec::value_type;
-      using _tags = detail::make_joined_set_t<detail::type_set<tag::is_column, tag::is_expression, tag::is_selectable>,
-                                              typename ColumnSpec::_traits::_tags>;
+      using _tags = detail::make_joined_set_t<detail::type_set<tag::is_column, tag::is_expression, tag::is_selectable>>;
     };
 
     using _nodes = detail::type_vector<>;
     using _required_tables = detail::type_set<Table>;
-    using _can_be_null = column_spec_can_be_null_t<ColumnSpec>;
 
     using _spec_t = ColumnSpec;
     using _table = Table;
@@ -98,7 +96,7 @@ namespace sqlpp
 
     auto operator=(null_t /*unused*/) const -> assignment_t<column_t, null_t>
     {
-      static_assert(can_be_null_t<column_t>::value, "column cannot be null");
+      static_assert(can_be_null<column_t>::value, "column cannot be null");
       return {*this, null_t{}};
     }
 
diff --git a/include/sqlpp11/cte.h b/include/sqlpp11/cte.h
index c6e047a7..9cdf2ef3 100644
--- a/include/sqlpp11/cte.h
+++ b/include/sqlpp11/cte.h
@@ -94,8 +94,7 @@ namespace sqlpp
   {
     using _alias_t = typename FieldSpec::_alias_t;
 
-    using _traits = make_traits<value_type_of_t<FieldSpec>,
-                                tag_if<tag::can_be_null, column_spec_can_be_null_t<FieldSpec>::value>>;
+    using _traits = make_traits<value_type_of_t<FieldSpec>>;
   };
 
   template <typename AliasProvider, typename Statement, typename ResultRow>
diff --git a/include/sqlpp11/lower.h b/include/sqlpp11/lower.h
index f9ad1a4b..b0cd16ea 100644
--- a/include/sqlpp11/lower.h
+++ b/include/sqlpp11/lower.h
@@ -60,7 +60,6 @@ namespace sqlpp
     using _traits = make_traits<text, tag::is_expression, tag::is_selectable>;
 
     using _nodes = detail::type_vector<Expr>;
-    using _can_be_null = can_be_null_t<Expr>;
 
     using _auto_alias_t = lower_alias_t;
 
diff --git a/include/sqlpp11/operator/assign.h b/include/sqlpp11/operator/assign.h
index 444ff5ae..067b5d31 100644
--- a/include/sqlpp11/operator/assign.h
+++ b/include/sqlpp11/operator/assign.h
@@ -45,7 +45,7 @@ namespace sqlpp
 #warning handle default_t, but only if the column does have a default!
   template <typename L, typename R>
   using check_assign_args = std::enable_if_t<is_column_t<L>::value and values_are_comparable<L, R>::value and
-                                             (can_be_null_t<L>::value or not is_optional<R>::value) and
+                                             (can_be_null<L>::value or not is_optional<R>::value) and
                                              (has_default_t<L>::value or not std::is_same<R, default_value_t>::value)>;
 
   template <typename L, typename R, typename = check_assign_args<L, R>>
diff --git a/include/sqlpp11/select_pseudo_table.h b/include/sqlpp11/select_pseudo_table.h
index a2e55658..58ed1f4d 100644
--- a/include/sqlpp11/select_pseudo_table.h
+++ b/include/sqlpp11/select_pseudo_table.h
@@ -39,14 +39,14 @@ namespace sqlpp
   {
     using _alias_t = typename NamedExpr::_alias_t;
 
-    static constexpr bool _can_be_null = can_be_null_t<NamedExpr>::value;
     static constexpr bool _depends_on_outer_table =
         detail::make_intersect_set_t<required_tables_of<NamedExpr>, typename Select::_used_outer_tables>::size::value >
         0;
 
 #warning: somehow prevent insert...
-    using _traits = make_traits<value_type_of_t<NamedExpr>,
-                                tag_if<tag::can_be_null, _can_be_null or _depends_on_outer_table>>;
+#warning: may need to make value type optional for outer tables
+    using _traits = make_traits<value_type_of_t<NamedExpr>/*,
+                                tag_if<tag::can_be_null, _depends_on_outer_table>*/>;
   };
 
   template<typename... NamedExpr>
@@ -60,7 +60,6 @@ namespace sqlpp
   struct select_expression_type<NamedExpr> {
     using value_t = value_type_of_t<NamedExpr>;
     static constexpr bool _is_expression = true;
-    static constexpr bool _can_be_null = can_be_null_t<NamedExpr>::value;
   };
 
   template <typename Select, typename... NamedExpr>
@@ -72,7 +71,6 @@ namespace sqlpp
         // Usage as named expression
         typename _expr_t::value_t,
         tag_if<tag::is_expression, _expr_t::_is_expression>,
-        tag_if<tag::can_be_null, _expr_t::_can_be_null>,
         // Usage as table
         tag::is_table,
         tag::is_pseudo_table,
diff --git a/include/sqlpp11/statement.h b/include/sqlpp11/statement.h
index d9036a91..452eb5e2 100644
--- a/include/sqlpp11/statement.h
+++ b/include/sqlpp11/statement.h
@@ -138,9 +138,12 @@ namespace sqlpp
           make_traits<_value_type, tag_if<tag::is_expression, not std::is_same<_value_type, no_value_t>::value>>;
 
       using _nodes = detail::type_vector<>;
+#warning: maybe need to make value type optional
+      /*
       using _can_be_null = logic::any_t<can_be_null_t<_result_type_provider>::value,
                                         detail::make_intersect_set_t<required_tables_of<_result_type_provider>,
                                                                      _all_provided_outer_tables>::size::value != 0>;
+                                        */
       using _parameters = detail::type_vector_cat_t<parameters_of<Policies>...>;
       // required_tables and _required_ctes are defined above
 
diff --git a/include/sqlpp11/table_alias.h b/include/sqlpp11/table_alias.h
index 4d3bfda6..572a1cb3 100644
--- a/include/sqlpp11/table_alias.h
+++ b/include/sqlpp11/table_alias.h
@@ -44,7 +44,6 @@ namespace sqlpp
     using _traits = make_traits<value_type_of_t<Table>,
                                 tag::is_table,
                                 tag::is_alias,
-                                tag_if<tag::can_be_null, can_be_null_t<Table>::value>,
                                 tag_if<tag::is_selectable, is_expression_t<Table>::value>>;
 
     using _nodes = detail::type_vector<>;
diff --git a/include/sqlpp11/trim.h b/include/sqlpp11/trim.h
index 3eec5492..664392f0 100644
--- a/include/sqlpp11/trim.h
+++ b/include/sqlpp11/trim.h
@@ -61,7 +61,6 @@ namespace sqlpp
     using _traits = make_traits<text, tag::is_expression, tag::is_selectable>;
 
     using _nodes = detail::type_vector<Expr>;
-    using _can_be_null = can_be_null_t<Expr>;
 
     using _auto_alias_t = trim_alias_t;
 
diff --git a/include/sqlpp11/type_traits.h b/include/sqlpp11/type_traits.h
index c8bc0281..c0ea2abf 100644
--- a/include/sqlpp11/type_traits.h
+++ b/include/sqlpp11/type_traits.h
@@ -412,30 +412,8 @@ namespace sqlpp
   template <typename T>
   using is_day_or_time_point_t = logic::any_t<is_day_point_t<T>::value, is_time_point_t<T>::value>;
 
-  namespace tag
-  {
-    struct can_be_null
-    {
-    };
-  }  // namespace tag
-
-  namespace detail
-  {
-    template <typename T, typename Enable = void>
-    struct column_spec_can_be_null_impl
-    {
-      using type = std::false_type;
-    };
-    template <typename T>
-    struct column_spec_can_be_null_impl<
-        T,
-        typename std::enable_if<detail::is_element_of<tag::can_be_null, typename T::_traits::_tags>::value>::type>
-    {
-      using type = std::true_type;
-    };
-  }  // namespace detail
   template <typename T>
-  using column_spec_can_be_null_t = typename detail::column_spec_can_be_null_impl<T>::type;
+  struct can_be_null : public is_optional<value_type_of_t<T>> {};
 
 #define SQLPP_VALUE_TRAIT_GENERATOR(name)                                                                   \
   namespace tag                                                                                             \
@@ -597,7 +575,6 @@ namespace sqlpp
   template <typename T>                                               \
   using trait##_t = typename detail::trait##_impl<T>::type;
 
-  SQLPP_RECURSIVE_TRAIT_GENERATOR(can_be_null)
   SQLPP_RECURSIVE_TRAIT_GENERATOR(contains_aggregate_function)
 
   template <typename ValueType, typename T>
diff --git a/include/sqlpp11/upper.h b/include/sqlpp11/upper.h
index 0b26221e..6059071a 100644
--- a/include/sqlpp11/upper.h
+++ b/include/sqlpp11/upper.h
@@ -60,7 +60,6 @@ namespace sqlpp
     using _traits = make_traits<text, tag::is_expression, tag::is_selectable>;
 
     using _nodes = detail::type_vector<Expr>;
-    using _can_be_null = can_be_null_t<Expr>;
 
     using _auto_alias_t = upper_alias_t;
 
diff --git a/scripts/ddl2cpp b/scripts/ddl2cpp
index 7e154366..517b1753 100755
--- a/scripts/ddl2cpp
+++ b/scripts/ddl2cpp
@@ -703,8 +703,6 @@ def createHeader():
                 )
                 print("You can disable this warning using -no-timestamp-warning")
                 noTimestampWarning = True
-            traitslist = ["::sqlpp::" + columnType]
-            columnCanBeNull = not column.notNull and not column.isPrimaryKey
             print("    struct " + columnClass, file=header)
             print("    {", file=header)
             print("      struct _alias_t", file=header)
@@ -735,21 +733,19 @@ def createHeader():
             )
             print("          };", file=header)
             print("      };", file=header)
-            hasAutoValue = column.hasAutoValue or (autoId and sqlColumnName == "id")
-            if columnCanBeNull:
-                traitslist.append("::sqlpp::tag::can_be_null")
-            if column.hasDefaultValue or hasAutoValue or columnCanBeNull:
-                traitslist.append("::sqlpp::tag::has_default")
+            columnCanBeNull = not column.notNull and not column.isPrimaryKey
             if columnCanBeNull:
                 print("      using value_type = ::sqlpp::compat::optional<::sqlpp::" + columnType + ">;", file=header)
             else:
                 print("      using value_type = ::sqlpp::" + columnType + ";", file=header)
-            print(
-                "      using _traits = ::sqlpp::make_traits<"
-                + ", ".join(traitslist)
-                + ">;",
-                file=header,
-            )
+            columnHasDefault = column.hasDefaultValue or \
+                               columnCanBeNull or \
+                               column.hasAutoValue or \
+                               (autoId and sqlColumnName == "id")
+            if columnHasDefault:
+              print("      using has_default_value = std::true_type;", file=header)
+            else:
+              print("      using has_default_value = std::false_type;", file=header)
             print("    };", file=header)
         print("  } // namespace " + tableNamespace, file=header)
         print("", file=header)
diff --git a/tests/core/types/result_row.cpp b/tests/core/types/result_row.cpp
index e0da2af1..c82253bb 100644
--- a/tests/core/types/result_row.cpp
+++ b/tests/core/types/result_row.cpp
@@ -44,12 +44,12 @@ namespace
 
 int main()
 {
-  static_assert(not sqlpp::can_be_null_t<decltype(bar.id)>::value, "");
-  static_assert(sqlpp::can_be_null_t<decltype(foo.doubleN)>::value, "");
-  static_assert(not sqlpp::can_be_null_t<decltype(foo.textNnD)>::value, "");
-  static_assert(not sqlpp::can_be_null_t<decltype(bar.boolNn)>::value, "");
+  static_assert(not sqlpp::can_be_null<decltype(bar.id)>::value, "");
+  static_assert(sqlpp::can_be_null<decltype(foo.doubleN)>::value, "");
+  static_assert(not sqlpp::can_be_null<decltype(foo.textNnD)>::value, "");
+  static_assert(not sqlpp::can_be_null<decltype(bar.boolNn)>::value, "");
   const auto seven = sqlpp::value(7).as(sqlpp::alias::s);
-  static_assert(not sqlpp::can_be_null_t<decltype(seven)>::value, "");
+  static_assert(not sqlpp::can_be_null<decltype(seven)>::value, "");
 
   // Select non-optional column or alias of it.
   for (const auto& row : db(select(foo.id, foo.id.as(sqlpp::alias::a), foo.textNnD, foo.textNnD.as(sqlpp::alias::b))
@@ -319,8 +319,8 @@ int main()
       // aggregates of nullable values
 #warning use a nullable value
       const auto a = bar.id;
-      static_assert(not sqlpp::can_be_null_t<decltype(bar.id)>::value, "");
-      static_assert(not sqlpp::can_be_null_t<decltype(a)>::value, "");
+      static_assert(not sqlpp::can_be_null<decltype(bar.id)>::value, "");
+      static_assert(not sqlpp::can_be_null<decltype(a)>::value, "");
       const auto rows = db(select(count(a), avg(a), max(a), min(a), sum(a)).from(bar).unconditionally());
       auto& x = rows.front();
       static_assert(not is_optional<decltype(x.count)>::value, "");
@@ -332,8 +332,8 @@ int main()
     {
       // aggregates of nullable values
       const auto o = foo.doubleN;
-      static_assert(sqlpp::can_be_null_t<decltype(foo.doubleN)>::value, "");
-      static_assert(sqlpp::can_be_null_t<decltype(o)>::value, "");
+      static_assert(sqlpp::can_be_null<decltype(foo.doubleN)>::value, "");
+      static_assert(sqlpp::can_be_null<decltype(o)>::value, "");
       const auto rows = db(select(count(o), avg(o), max(o), min(o), sum(o)).from(foo).unconditionally());
       auto& x = rows.front();
       static_assert(not is_optional<decltype(x.count)>::value, "");
diff --git a/tests/core/usage/Sample.h b/tests/core/usage/Sample.h
index 890724e5..220e9a28 100644
--- a/tests/core/usage/Sample.h
+++ b/tests/core/usage/Sample.h
@@ -25,7 +25,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::integer;
-      using _traits = ::sqlpp::make_traits<::sqlpp::integer, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct TextNnD
     {
@@ -42,7 +42,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::text;
-      using _traits = ::sqlpp::make_traits<::sqlpp::text, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct IntN
     {
@@ -59,7 +59,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::integer>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::integer, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct DoubleN
     {
@@ -76,7 +76,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::floating_point>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::floating_point, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct UIntN
     {
@@ -93,7 +93,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::integer_unsigned>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::integer_unsigned, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct BlobN
     {
@@ -110,7 +110,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::blob>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::blob, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
   } // namespace TabFoo_
 
@@ -152,7 +152,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::integer;
-      using _traits = ::sqlpp::make_traits<::sqlpp::integer, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct TextN
     {
@@ -169,7 +169,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::text>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::text, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct BoolNn
     {
@@ -186,7 +186,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::boolean;
-      using _traits = ::sqlpp::make_traits<::sqlpp::boolean>;
+      using has_default_value = std::false_type;
     };
     struct IntN
     {
@@ -203,7 +203,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::integer>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::integer, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
   } // namespace TabBar_
 
@@ -243,7 +243,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::integer;
-      using _traits = ::sqlpp::make_traits<::sqlpp::integer, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct DayPointN
     {
@@ -260,7 +260,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::day_point>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::day_point, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct TimePointN
     {
@@ -277,7 +277,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::time_point>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::time_point, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
     struct TimeOfDayN
     {
@@ -294,7 +294,7 @@ namespace test
           };
       };
       using value_type = ::sqlpp::compat::optional<::sqlpp::time_of_day>;
-      using _traits = ::sqlpp::make_traits<::sqlpp::time_of_day, ::sqlpp::tag::can_be_null, ::sqlpp::tag::has_default>;
+      using has_default_value = std::true_type;
     };
   } // namespace TabDateTime_