Follow outer tables through the statement.

This is important to determine which result column of a select can be
NULL.

include/sqlpp11/column.h

@@ -55,6 +55,7 @@ namespace sqlpp
 		{
 			using _parameters = std::tuple<>;
 			using _provided_tables = detail::type_set<>;
+			using _provided_outer_tables = detail::type_set<>;
 			using _required_tables = detail::type_set<Table>;
 			using _extra_tables = detail::type_set<>;
 			using _can_be_null = column_spec_can_be_null_t<ColumnSpec>;

include/sqlpp11/extra_tables.h

@@ -56,6 +56,7 @@ namespace sqlpp
 			{
 				using _parameters = std::tuple<>;
 				using _required_tables = ::sqlpp::detail::type_set<>;
+				using _provided_outer_tables = ::sqlpp::detail::type_set<>;
 				using _provided_tables = ::sqlpp::detail::type_set<>;
 				using _extra_tables = ::sqlpp::detail::type_set<Tables...>;
 				using _can_be_null = std::false_type;

include/sqlpp11/join.h

@@ -35,41 +35,29 @@ namespace sqlpp
 {
 	struct inner_join_t
 	{
-		template<typename Db>
+		template<typename Lhs, typename Rhs>
-			struct _is_supported 
+			using _provided_outer_tables = detail::make_joined_set<provided_outer_tables_of<Lhs>, provided_outer_tables_of<Rhs>>;
-			{ 
-				static constexpr bool value = Db::_supports_inner_join; 
-			};
 
 		static constexpr const char* _name = " INNER ";
 	};
 	struct outer_join_t
 	{
-		template<typename Db>
+		template<typename Lhs, typename Rhs>
-			struct _is_supported 
+			using _provided_outer_tables = detail::make_joined_set<provided_tables_of<Lhs>, provided_tables_of<Rhs>>;
-			{ 
-				static constexpr bool value = Db::_supports_outer_join; 
-			};
 
 		static constexpr const char* _name = " OUTER ";
 	};
 	struct left_outer_join_t
 	{
-		template<typename Db>
+		template<typename Lhs, typename Rhs>
-			struct _is_supported 
+			using _provided_outer_tables = detail::make_joined_set<provided_outer_tables_of<Lhs>, provided_tables_of<Rhs>>;
-			{ 
-				static constexpr bool value = Db::_supports_left_outer_join; 
-			};
 
 		static constexpr const char* _name = " LEFT OUTER ";
 	};
 	struct right_outer_join_t
 	{
-		template<typename Db>
+		template<typename Lhs, typename Rhs>
-			struct _is_supported 
+			using _provided_outer_tables = detail::make_joined_set<provided_tables_of<Lhs>, provided_outer_tables_of<Rhs>>;
-			{ 
-				static constexpr bool value = Db::_supports_right_outer_join; 
-			};
 
 		static constexpr const char* _name = " RIGHT OUTER ";
 	};
@@ -78,7 +66,16 @@ namespace sqlpp
 		struct join_t
 		{
 			using _traits = make_traits<no_value_t, tag::table, tag::join>;
-			using _recursive_traits = make_recursive_traits<Lhs, Rhs>;
+			struct _recursive_traits
+			{
+				using _required_tables = detail::make_joined_set_t<required_tables_of<Lhs>, required_tables_of<Rhs>>;
+				using _provided_tables = detail::make_joined_set_t<provided_tables_of<Lhs>, provided_tables_of<Rhs>>;
+				using _provided_outer_tables = typename JoinType::template _provided_outer_tables<Lhs, Rhs>;
+				using _extra_tables = detail::make_joined_set_t<extra_tables_of<Lhs>, extra_tables_of<Rhs>>;
+				using _parameters = detail::make_parameter_tuple_t<parameters_of<Lhs>, parameters_of<Rhs>>;
+				using _can_be_null = std::false_type;
+			};
+
 
 			static_assert(is_table_t<Lhs>::value, "lhs argument for join() has to be a table or join");
 			static_assert(is_table_t<Rhs>::value, "rhs argument for join() has to be a table");

include/sqlpp11/parameter.h

@@ -41,6 +41,7 @@ namespace sqlpp
 		{
 			using _parameters = std::tuple<parameter_t>;
 			using _provided_tables = detail::type_set<>;
+			using _provided_outer_tables = detail::type_set<>;
 			using _required_tables = detail::type_set<>;
 			using _extra_tables = detail::type_set<>;
 			using _can_be_null = std::true_type;

include/sqlpp11/select_pseudo_table.h

@@ -35,6 +35,7 @@ namespace sqlpp
 	template<typename NamedExpr>
 		struct select_column_spec_t
 		{
+#warning use Select here to determine if a column relates to a outer join table
 			using _name_t = typename NamedExpr::_name_t;
 
 			using _traits = make_traits<value_type_of<NamedExpr>, 

include/sqlpp11/statement.h

@@ -63,6 +63,7 @@ namespace sqlpp
 
 				using _all_required_tables = detail::make_joined_set_t<required_tables_of<Policies>...>;
 				using _all_provided_tables = detail::make_joined_set_t<provided_tables_of<Policies>...>;
+				using _all_provided_outer_tables = detail::make_joined_set_t<provided_outer_tables_of<Policies>...>;
 				using _all_extra_tables = detail::make_joined_set_t<extra_tables_of<Policies>...>;
 
 				using _known_tables = detail::make_joined_set_t<_all_provided_tables, _all_extra_tables>;
@@ -108,6 +109,7 @@ namespace sqlpp
 				{
 					using _required_tables = statement_policies_t::_required_tables;
 					using _provided_tables = detail::type_set<>;
+					using _provided_outer_tables = detail::type_set<>;
 					using _extra_tables = detail::type_set<>;
 					using _parameters = detail::make_parameter_tuple_t<parameters_of<Policies>...>;
 					using _can_be_null = detail::any_t<can_be_null_t<_value_type>::value>;
@@ -128,6 +130,7 @@ namespace sqlpp
 
 		using _traits = make_traits<value_type_of<_policies_t>, ::sqlpp::tag::select, tag::expression_if<typename _policies_t::_is_expression>, tag::named_expression_if<typename _policies_t::_is_expression>>;
 		using _recursive_traits = typename _policies_t::_recursive_traits;
+		using _used_outer_tables = typename _policies_t::_all_provided_outer_tables;
 
 		using _result_type_provider = typename _policies_t::_result_type_provider;
 

include/sqlpp11/table.h

@@ -49,6 +49,7 @@ namespace sqlpp
 			using _parameters = std::tuple<>;
 			using _required_tables = detail::type_set<>;
 			using _provided_tables = detail::type_set<Table>;
+			using _provided_outer_tables = detail::type_set<>;
 			using _extra_tables = detail::type_set<>;
 			using _can_be_null = std::false_type;
 		};

include/sqlpp11/table_alias.h

@@ -46,6 +46,7 @@ namespace sqlpp
 			using _parameters = std::tuple<>;
 			using _required_tables = detail::type_set<>;
 			using _provided_tables = detail::type_set<AliasProvider>;
+			using _provided_outer_tables = detail::type_set<>;
 			using _extra_tables = detail::type_set<>;
 			using _can_be_null = std::false_type;
 		};

include/sqlpp11/type_traits.h

@@ -202,6 +202,12 @@ namespace sqlpp
 				using type = typename T::_recursive_traits::_provided_tables;
 			};
 
+		template<typename T>
+			struct provided_outer_table_of_impl
+			{
+				using type = typename T::_recursive_traits::_provided_outer_tables;
+			};
+
 		template<typename T>
 			struct extra_table_of_impl
 			{
@@ -238,6 +244,9 @@ namespace sqlpp
 	template<typename T>
 		using provided_tables_of = typename detail::provided_table_of_impl<T>::type;
 
+	template<typename T>
+		using provided_outer_tables_of = typename detail::provided_outer_table_of_impl<T>::type;
+
 	template<typename T>
 		using extra_tables_of = typename detail::extra_table_of_impl<T>::type;
 
@@ -258,6 +267,7 @@ namespace sqlpp
 		{
 			using _required_tables = detail::make_joined_set_t<required_tables_of<Arguments>...>;
 			using _provided_tables = detail::make_joined_set_t<provided_tables_of<Arguments>...>;
+			using _provided_outer_tables = detail::make_joined_set_t<provided_outer_tables_of<Arguments>...>;
 			using _extra_tables = detail::make_joined_set_t<extra_tables_of<Arguments>...>;
 			using _parameters = detail::make_parameter_tuple_t<parameters_of<Arguments>...>;
 			using _can_be_null = detail::any_t<can_be_null_t<Arguments>::value...>;