Started to rewrite traits and recursive traits

traits are shorter and easier to identify by using tags in a variadic
template

recursive traits can be automatically derived, which makes it much
easier to add new traits to be handed through the expression tree.

include/sqlpp11/alias.h

@@ -33,18 +33,13 @@ namespace sqlpp
 	template<typename Expression, typename AliasProvider>
 		struct expression_alias_t
 		{
+			using _traits = make_traits_t<value_type_of<Expression>, tag::named_expression>;
+			using _recursive_traits = make_recursive_traits_t<Expression>;
+
 			static_assert(is_expression_t<Expression>::value, "invalid argument for an expression alias");
 			static_assert(not is_alias_t<Expression>::value, "cannot create an alias of an alias");
 
-			struct _value_type: Expression::_value_type
-			{
-				using _is_expression = std::false_type;
-				using _is_named_expression = std::true_type;
-				using _is_alias = std::true_type;
-			};
-
 			using _name_t = typename AliasProvider::_name_t;
-			using _table_set = typename Expression::_table_set;
 
 			Expression _expression;
 		};

include/sqlpp11/any.h

@@ -37,11 +37,8 @@ namespace sqlpp
 		template<typename Select>
 		struct any_t
 		{
-			struct _value_type: public Select::_value_type::_base_value_type
+			using _traits = make_traits_t<value_type_of<Select>, tag::multi_expression>;
-			{
+			using _recursive_traits = make_recursive_traits_t<Select>;
-				using _is_expression = std::false_type;
-				using _is_multi_expression = std::true_type; // must not be named or used with +,-,*,/, etc
-			};
 
 			struct _name_t
 			{
@@ -55,8 +52,6 @@ namespace sqlpp
 					};
 			};
 
-			using _table_set = typename Select::_table_set;
-
 			any_t(Select select):
 				_select(select)
 			{}

include/sqlpp11/avg.h

@@ -36,16 +36,12 @@ namespace sqlpp
 		template<typename Flag, typename Expr>
 		struct avg_t: public floating_point::template expression_operators<avg_t<Flag, Expr>>
 		{
+			using _traits = make_traits_t<value_type_of<Expr>, tag::expression, tag::named_expression>;
+			using _recursive_traits = make_recursive_traits_t<Select>;
+
 			static_assert(is_noop<Flag>::value or std::is_same<sqlpp::distinct_t, Flag>::value, "avg() used with flag other than 'distinct'");
 			static_assert(is_numeric_t<Expr>::value, "avg() requires a value expression as argument");
 
-			struct _value_type: public floating_point
-			{
-				using _is_named_expression = std::true_type;
-			};
-
-			using _table_set = typename Expr::_table_set;
-
 			struct _name_t
 			{
 				static constexpr const char* _get_name() { return "AVG"; }

include/sqlpp11/boolean.h

@@ -42,16 +42,11 @@ namespace sqlpp
 		// boolean value type
 		struct boolean
 		{
-			using _value_type = boolean;
-			using _base_value_type = boolean;
-			using _is_boolean = std::true_type;
-			using _is_value = std::true_type;
-			using _is_expression = std::true_type;
 			using _cpp_value_type = bool;
 
 			struct _parameter_t
 			{
-				using _value_type = boolean;
+				using _value_type = boolean; // FIXME
 
 				_parameter_t():
 					_value(false),

include/sqlpp11/column.h

@@ -45,21 +45,20 @@ namespace sqlpp
 	struct column_t: public ColumnSpec::_value_type::template expression_operators<column_t<Table, ColumnSpec>>,
 	                 public ColumnSpec::_value_type::template column_operators<column_t<Table, ColumnSpec>>
 	{ 
-		using _is_column = std::true_type;
+		using _traits = make_traits_t<value_type_of<ColumnSpec>, tag::column, tag::expression, tag::named_expression>;
+		struct _recursive_traits
+		{
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = detail::type_set<_table>;
+		};
+
 		using _spec_t = ColumnSpec;
 		using _table = Table;
-		using _table_set = detail::type_set<_table>;
+		using _column_type = typename _spec_t::_column_type;
-		using _column_type = typename ColumnSpec::_column_type;
+		using _name_t = typename _spec_t::_name_t;
-		struct _value_type: ColumnSpec::_value_type
-		{
-			using _is_expression = std::true_type;
-			using _is_named_expression = std::true_type;
-			using _is_alias = std::false_type;
-		};
-		template<typename T>
-			using _is_valid_operand = typename _value_type::template _is_valid_operand<T>;
 
-		using _name_t = typename ColumnSpec::_name_t;
+		template<typename T>
+			using _is_valid_operand = typename value_type_of<ColumnSpec>::template _is_valid_operand<T>;
 
 		column_t() = default;
 		column_t(const column_t&) = default;

include/sqlpp11/count.h

@@ -37,16 +37,12 @@ namespace sqlpp
 		template<typename Flag, typename Expr>
 		struct count_t: public sqlpp::detail::integral::template expression_operators<count_t<Flag, Expr>>
 		{
+			using _traits = make_traits_t<value_type_of<Expr>, tag::expression, tag::named_expression>;
+			using _recursive_traits = make_recursive_traits_t<Select>;
+
 			static_assert(is_noop<Flag>::value or std::is_same<sqlpp::distinct_t, Flag>::value, "count() used with flag other than 'distinct'");
 			static_assert(is_expression_t<Expr>::value, "count() requires a sql expression as argument");
 
-			struct _value_type: public sqlpp::detail::integral
-			{
-				using _is_named_expression = std::true_type;
-			};
-
-			using _table_set = typename Expr::_table_set;
-
 			struct _name_t
 			{
 				static constexpr const char* _get_name() { return "COUNT"; }

include/sqlpp11/default_value.h

@@ -33,9 +33,8 @@ namespace sqlpp
 {
 	struct default_value_t
 	{
-		static constexpr bool _is_expression = true;
+		using _traits = make_traits_t<no_value_t, tag::expression>;
-		using _value_type = no_value_t;
+		using _recursive_traits = make_recursive_traits_t<>;
-		using _table_set = ::sqlpp::detail::type_set<>;
 
 		static constexpr bool _is_trivial() { return false; }
 	};

include/sqlpp11/exists.h

@@ -36,15 +36,11 @@ namespace sqlpp
 		template<typename Select>
 		struct exists_t: public boolean::template expression_operators<exists_t<Select>>
 		{
+			using _traits = make_traits_t<boolean, tag::expression, tag::named_expression>;
+			using _recursive_traits = make_recursive_traits_t<Select>;
+
 			static_assert(is_select_t<Select>::value, "exists() requires a select expression as argument");
 
-			struct _value_type: public boolean
-			{
-				using _is_named_expression = std::true_type;
-			};
-
-			using _table_set = typename Select::_table_set;
-
 			struct _name_t
 			{
 				static constexpr const char* _get_name() { return "EXISTS"; }

include/sqlpp11/floating_point.h

@@ -41,17 +41,11 @@ namespace sqlpp
 		// floating_point value type
 		struct floating_point
 		{
-			using _value_type = floating_point;
-			using _base_value_type = floating_point;
-			using _is_numeric = std::true_type;
-			using _is_floating_point = std::true_type;
-			using _is_value = std::true_type;
-			using _is_expression = std::true_type;
 			using _cpp_value_type = double;
 			
 			struct _parameter_t
 			{
-				using _value_type = integral;
+				using _value_type = floating_point;
 
 				_parameter_t():
 					_value(0),

include/sqlpp11/functions.h

@@ -48,7 +48,8 @@ namespace sqlpp
 	template<typename T>
 		auto value(T t) -> vendor::wrap_operand_t<T>
 		{
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 			static_assert(not is_value_t<T>::value, "value() is to be called with non-sql-type like int, or string");
 			return { t };
 		}
@@ -56,8 +57,8 @@ namespace sqlpp
 	template<typename ValueType> // Csaba Csoma suggests: unsafe_sql instead of verbatim
 	struct verbatim_t: public ValueType::template expression_operators<verbatim_t<ValueType>>
 	{
-		using _value_type = ValueType;
+		using _traits = make_traits_t<ValueType, tag::expression>;
-		using _table_set = ::sqlpp::detail::type_set<>;
+		using _recursive_traits = make_recursive_traits_t<Select>;
 
 		verbatim_t(std::string verbatim): _verbatim(verbatim) {}
 		verbatim_t(const verbatim_t&) = default;
@@ -102,9 +103,10 @@ namespace sqlpp
 	template<typename Container>
 		struct value_list_t // to be used in .in() method
 		{
+			using _traits = make_traits_t<vendor::value_type_t<typename _container_t::value_type>;
+			using _recursive_traits = make_recursive_traits_t<Select>;
+
 			using _container_t = Container;
-			using _table_set = ::sqlpp::detail::type_set<>;// FIXME: Could it be something else?
-			using _value_type = vendor::value_type_t<typename _container_t::value_type>;
 
 			value_list_t(_container_t container):
 				_container(container)

include/sqlpp11/integral.h

@@ -42,14 +42,7 @@ namespace sqlpp
 		// integral value type
 		struct integral
 		{
-			using _value_type = integral;
-			using _base_value_type = integral;
-			using _is_numeric = std::true_type;
-			using _is_integral = std::true_type;
-			using _is_value = std::true_type;
-			using _is_expression = std::true_type;
 			using _cpp_value_type = int64_t;
-
 			
 			struct _parameter_t
 			{

include/sqlpp11/join.h

@@ -77,16 +77,17 @@ namespace sqlpp
 	template<typename JoinType, typename Lhs, typename Rhs, typename On = vendor::noop>
 		struct join_t
 		{
+			using _traits = make_traits_t<no_value_t, tag::table, tag::join>;
+			using _recursive_traits = make_recursive_traits_t<Lhs, Rhs>;
+
 			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");
 			static_assert(not is_join_t<Rhs>::value, "rhs argument for join must not be a join");
 			static_assert(vendor::is_noop<On>::value or is_on_t<On>::value, "invalid on expression in join().on()");
 
-			static_assert(::sqlpp::detail::is_disjunct_from<typename Lhs::_table_set, typename Rhs::_table_set>::value, "joined tables must not be identical");
+			static_assert(::sqlpp::detail::is_disjunct_from<typename Lhs::_provided_tables, typename Rhs::_provided_tables>::value, "joined tables must not be identical");
 
-			using _is_table = std::true_type;
+			static_assert(_recursive_traits::_required_tables::size::value == 0, "joined tables must not depend on other tables");
-			using _is_join = std::true_type;
-			using _table_set = typename ::sqlpp::detail::make_joined_set<typename Lhs::_table_set, typename Rhs::_table_set>::type;
 
 			template<typename OnT> 
 				using set_on_t = join_t<JoinType, Lhs, Rhs, OnT>;

include/sqlpp11/max.h

@@ -36,15 +36,11 @@ namespace sqlpp
 		template<typename Expr>
 		struct max_t: public Expr::_value_type::template expression_operators<max_t<Expr>>
 		{
+			using _traits = make_traits_t<value_type_of<Expr>, tag::expression, tag::named_expression>;
+			using _recursive_traits = make_recursive_traits_t<Select>;
+
 			static_assert(is_value_t<Expr>::value, "max() requires a value expression as argument");
 
-			struct _value_type: public Expr::_value_type::_base_value_type
-			{
-				using _is_named_expression = std::true_type;
-			};
-
-			using _table_set = typename Expr::_table_set;
-
 			struct _name_t
 			{
 				static constexpr const char* _get_name() { return "MAX"; }

include/sqlpp11/min.h

@@ -36,15 +36,11 @@ namespace sqlpp
 		template<typename Expr>
 		struct min_t: public Expr::_value_type::template expression_operators<min_t<Expr>>
 		{
+			using _traits = make_traits_t<value_type_of<Expr>, tag::expression, tag::named_expression>;
+			using _recursive_traits = make_recursive_traits_t<Select>;
+
 			static_assert(is_value_t<Expr>::value, "min() requires a value expression as argument");
 
-			struct _value_type: public Expr::_value_type::_base_value_type
-			{
-				using _is_named_expression = std::true_type;
-			};
-
-			using _table_set = typename Expr::_table_set;
-
 			struct _name_t
 			{
 				static constexpr const char* _get_name() { return "MIN"; }

include/sqlpp11/multi_column.h

@@ -41,9 +41,10 @@ namespace sqlpp
 	template<typename Unused, typename... Columns>
 		struct multi_column_t
 		{
-			static_assert(detail::all_t<is_named_expression_t<Columns>::value...>::value, "multi_column parameters need to be named expressions");
+			using _traits = make_traits_t<no_value_t>;
+			using _recursive_traits = make_recursive_traits_t<Columns...>;
 
-			using _table_set = sqlpp::detail::make_joined_set_t<typename Columns::_table_set...>;
+			static_assert(detail::all_t<is_named_expression_t<Columns>::value...>::value, "multi_column parameters need to be named expressions");
 
 			multi_column_t(std::tuple<Columns...> columns):
 				_columns(columns)
@@ -75,10 +76,12 @@ namespace sqlpp
 	template<typename AliasProvider, typename... Columns>
 		struct multi_column_alias_t
 		{
+			using _traits = make_traits_t<no_value_t, alias>;
+			using _recursive_traits = make_recursive_traits_t<Columns...>;
+
 			static_assert(detail::all_t<is_named_expression_t<Columns>::value...>::value, "multi_column parameters need to be named expressions");
 
 			using _name_t = typename AliasProvider::_name_t;
-			using _table_set = sqlpp::detail::make_joined_set_t<typename Columns::_table_set...>;
 
 			multi_column_alias_t(multi_column_t<void, Columns...> multi_column):
 				_columns(multi_column._columns)

include/sqlpp11/no_value.h

@@ -33,11 +33,6 @@ namespace sqlpp
 {
 	struct no_value_t
 	{
-		template<typename T>
-			using _constraint = std::false_type;
-
-		using _base_value_type = no_value_t;
-
 		template<typename T>
 			struct _is_valid_operand
 			{

include/sqlpp11/null.h

@@ -33,9 +33,8 @@ namespace sqlpp
 {
 	struct null_t
 	{
-		static constexpr bool _is_expression = true;
+		using _traits = make_traits_t<no_value_t, tag::expression>;
-		using _value_type = no_value_t;
+		using _recursive_traits = make_recursive_traits_t<>;
-		using _table_set = ::sqlpp::detail::type_set<>;
 	};
 
 	namespace vendor

include/sqlpp11/on.h

@@ -37,7 +37,9 @@ namespace sqlpp
 	template<typename Database, typename... Expr>
 		struct on_t
 		{
-			using _is_on = std::true_type;
+			using _traits = make_traits_t<no_value_t, tag::on>;
+			using _recursive_traits = make_recursive_traits_t<Expr...>;
+
 			using _is_dynamic = typename std::conditional<std::is_same<Database, void>::value, std::false_type, std::true_type>::type;
 
 			static_assert(_is_dynamic::value or sizeof...(Expr), "at least one expression argument required in on()");

include/sqlpp11/parameter.h

@@ -36,14 +36,10 @@ namespace sqlpp
 	template<typename ValueType, typename NameType>
 	struct parameter_t: public ValueType::template expression_operators<parameter_t<ValueType, NameType>>
 	{
-		struct _value_type: public ValueType
+		using _traits = make_traits_t<ValueType, tag::parameter, tag::expression>;
-		{
+		using _recursive_traits = make_recursive_traits_t<>;
-			using _is_expression = std::true_type;
+
-			using _is_alias = std::false_type;
-		};
-		using _is_parameter = std::true_type;
 		using _instance_t = typename NameType::_name_t::template _member_t<typename ValueType::_parameter_t>;
-		using _table_set = sqlpp::detail::type_set<>;
 
 		parameter_t()
 		{}

include/sqlpp11/result_row.h

@@ -42,9 +42,9 @@ namespace sqlpp
 
 		template<typename Db, std::size_t index, typename NamedExpr>
 			struct result_field:
-				public NamedExpr::_name_t::template _member_t<typename NamedExpr::_value_type::template _result_entry_t<Db, NamedExpr::_trivial_value_is_null>>
+				public NamedExpr::_name_t::template _member_t<typename value_type_of<NamedExpr>::template _result_entry_t<Db, NamedExpr::_trivial_value_is_null>>
 			{
-				using _field = typename NamedExpr::_name_t::template _member_t<typename NamedExpr::_value_type::template _result_entry_t<Db, NamedExpr::_trivial_value_is_null>>;
+				using _field = typename NamedExpr::_name_t::template _member_t<typename value_type_of<NamedExpr>::template _result_entry_t<Db, NamedExpr::_trivial_value_is_null>>;
 
 				result_field() = default;
 				result_field(const char_result_row_t& char_result_row_t):

include/sqlpp11/select_flags.h

@@ -37,11 +37,8 @@ namespace sqlpp
 	// standard select flags
 	struct all_t
 	{
-		struct _value_type 
+		using _traits = make_traits_t<no_value_t, tag::select_flag>;
-		{ 
+		using _recursive_traits = make_recursive_traits_t<>;
-			using _is_select_flag = std::true_type; 
-		};
-		using _table_set = detail::type_set<>;
 	};
 	static constexpr all_t all = {};
 
@@ -60,11 +57,8 @@ namespace sqlpp
 
 	struct distinct_t
 	{
-		struct _value_type 
+		using _traits = make_traits_t<no_value_t, tag::select_flag>;
-		{ 
+		using _recursive_traits = make_recursive_traits_t<>;
-			using _is_select_flag = std::true_type; 
-		};
-		using _table_set = detail::type_set<>;
 	};
 	static constexpr distinct_t distinct = {};
 
@@ -83,11 +77,8 @@ namespace sqlpp
 
 	struct straight_join_t
 	{
-		struct _value_type 
+		using _traits = make_traits_t<no_value_t, tag::select_flag>;
-		{ 
+		using _recursive_traits = make_recursive_traits_t<>;
-			using _is_select_flag = std::true_type; 
-		};
-		using _table_set = detail::type_set<>;
 	};
 	static constexpr straight_join_t straight_join = {};
 

include/sqlpp11/some.h

@@ -37,11 +37,8 @@ namespace sqlpp
 		template<typename Select>
 		struct some_t
 		{
-			struct _value_type: public Select::_value_type::_base_value_type
+			using _traits = make_traits_t<value_type_of<Select>, tag::multi_expression>;
-			{
+			using _recursive_traits = make_recursive_traits_t<Select>;
-				using _is_expression = std::false_type;
-				using _is_multi_expression = std::true_type; // must not be named or used with +,-,*,/, etc
-			};
 
 			struct _name_t
 			{
@@ -54,7 +51,6 @@ namespace sqlpp
 						const T& operator()() const { return some; }
 					};
 			};
-			using _table_set = typename Select::_table_set;
 
 			some_t(Select select):
 				_select(select)

include/sqlpp11/sort_order.h

@@ -41,7 +41,8 @@ namespace sqlpp
 		struct sort_order_t
 		{
 			using _is_sort_order = std::true_type;
-			using _table_set = typename Expression::_table_set;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename Expression::_required_tables;
 
 			Expression _expression;
 		};

include/sqlpp11/sum.h

@@ -36,14 +36,12 @@ namespace sqlpp
 		template<typename Flag, typename Expr>
 		struct sum_t: public Expr::_value_type::template expression_operators<sum_t<Flag, Expr>>
 		{
+			using _traits = make_traits_t<value_type_of<Expr>, tag::expression, tag::named_expression>;
+			using _recursive_traits = make_recursive_traits_t<Select>;
+
 			static_assert(is_noop<Flag>::value or std::is_same<sqlpp::distinct_t, Flag>::value, "sum() used with flag other than 'distinct'");
 			static_assert(is_numeric_t<Expr>::value, "sum() requires a numeric expression as argument");
 
-			struct _value_type: public Expr::_value_type::_base_value_type
-			{
-				using _is_named_expression = std::true_type;
-			};
-
 			struct _name_t
 			{
 				static constexpr const char* _get_name() { return "SUM"; }

include/sqlpp11/table.h

@@ -42,14 +42,21 @@ namespace sqlpp
 	template<typename Table, typename... ColumnSpec>
 	struct table_t: public table_base_t, public ColumnSpec::_name_t::template _member_t<column_t<Table, ColumnSpec>>...
 	{
-		using _table_set = detail::type_set<Table>; // Hint need a type_set here to be similar to a join (which always represents more than one table)
+		using _traits = make_traits_t<no_value_t, tag::table>;
+
+		struct _recursive_traits
+		{
+			using _parameters = std::tuple<>;
+			using _required_tables = detail::type_set<>;
+			using _provided_tables = detail::type_set<Table>;
+		};
+
 		static_assert(sizeof...(ColumnSpec), "at least one column required per table");
 		using _required_insert_columns = typename detail::make_type_set_if<require_insert_t, column_t<Table, ColumnSpec>...>::type;
 		using _column_tuple_t = std::tuple<column_t<Table, ColumnSpec>...>;
 		template<typename AliasProvider>
 			using _alias_t = table_alias_t<AliasProvider, Table, ColumnSpec...>;
 
-		using _is_table = std::true_type;
 
 		template<typename T>
 			join_t<inner_join_t, Table, T> join(T t)

include/sqlpp11/table_alias.h

@@ -41,16 +41,17 @@ namespace sqlpp
 		struct table_alias_t: public table_alias_base_t, public ColumnSpec::_name_t::template _member_t<column_t<AliasProvider, ColumnSpec>>...
 	{
 		//FIXME: Need to add join functionality
-		using _is_table = std::true_type;
+		using _traits = make_traits_t<value_type_of<Table>, tag::table, tag::alias, tag::named_expression_if<tag::is_expression<Table>>;
-		using _table_set = detail::type_set<AliasProvider>;
 
-		struct _value_type: Table::_value_type
+		struct _recursive_traits
 		{
-			using _is_expression = std::false_type;
+			using _parameters = std::tuple<>;
-			using _is_named_expression = copy_type_trait<Table, is_value_t>;
+			using _required_tables = detail::type_set<>;
-			using _is_alias = std::true_type;
+			using _provided_tables = detail::type_set<Table>;
 		};
 
+		static_assert(Table::_required_tables::size::value == 0, "table aliases must not depend on external tables");
+
 		using _name_t = typename AliasProvider::_name_t;
 		using _column_tuple_t = std::tuple<column_t<Table, ColumnSpec>...>;
 

include/sqlpp11/text.h

@@ -41,11 +41,6 @@ namespace sqlpp
 		// text value type
 		struct text
 		{
-			using _value_type = text;
-			using _base_value_type = text;
-			using _is_text = std::true_type;
-			using _is_value = std::true_type;
-			using _is_expression = std::true_type;
 			using _cpp_value_type = std::string;
 
 			struct _parameter_t

include/sqlpp11/tvin.h

@@ -38,9 +38,8 @@ namespace sqlpp
 	template<typename Operand>
 		struct tvin_t
 		{
-			using _operand_t = Operand;
+			using _traits = make_traits_t<value_type_of<Operand>, tag::operand, tag::expression>;
-			using _value_type = typename _operand_t::_value_type;
+			using _recursive_traits = make_recursive_traits_t<Operand>;
-			using _table_set = typename _operand_t::_table_set;
 
 			tvin_t(Operand operand): 
 				_value(operand)
@@ -76,7 +75,8 @@ namespace sqlpp
 	template<typename T>
 		struct maybe_tvin_t
 		{
-			using _table_set = typename T::_table_set;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename T::_required_tables;
 			static constexpr bool _is_trivial()
 			{
 				return false;
@@ -97,7 +97,8 @@ namespace sqlpp
 	template<typename T>
 		struct maybe_tvin_t<tvin_t<T>>
 		{
-			using _table_set = typename T::_table_set;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename T::_required_tables;
 			bool _is_trivial() const
 			{
 				return _value._is_trivial();

include/sqlpp11/vendor/assignment.h

@@ -65,13 +65,18 @@ namespace sqlpp
 		template<typename Lhs, typename Rhs>
 			struct assignment_t
 			{
-				using _is_assignment = std::true_type;
+				struct _traits
-				using _column_t = Lhs;
+				{
-				using value_type = Rhs;
+					using _is_assignment = std::true_type;
-				using _parameter_tuple_t = std::tuple<_column_t, Rhs>;
+					using value_type = no_value;
-				using _table_set = typename ::sqlpp::detail::make_joined_set<typename Lhs::_table_set, typename Rhs::_table_set>::type;
+				};
 
-				static_assert(can_be_null_t<_column_t>::value ? true : not std::is_same<Rhs, null_t>::value, "column must not be null");
+				using _recursive_traits = make_recursive_traits_t<Lhs, Rhs>;
+
+				using _column_t = Lhs;
+				using _value_t = Lhs;
+
+				static_assert(can_be_null_t<_column_t>::value ? true : not std::is_same<_value_t, null_t>::value, "column must not be null");
 
 				assignment_t(_column_t lhs, value_type rhs):
 					_lhs(lhs), 
@@ -85,7 +90,7 @@ namespace sqlpp
 				~assignment_t() = default;
 
 				_column_t _lhs;
-				value_type _rhs;
+				_value_t _rhs;
 			};
 
 		template<typename Context, typename Lhs, typename Rhs>
@@ -115,15 +120,21 @@ namespace sqlpp
 		template<typename Lhs, typename Rhs>
 			struct assignment_t<Lhs, tvin_t<Rhs>>
 			{
+				struct _traits
+				{
+					using _is_assignment = std::true_type;
+					using value_type = no_value;
+				};
+
+				using _recursive_traits = make_recursive_traits_t<Lhs, Rhs>;
+
 				using _is_assignment = std::true_type;
 				using _column_t = Lhs;
-				using value_type = tvin_t<Rhs>;
+				using _value_t = tvin_t<Rhs>;
-				using _parameter_tuple_t = std::tuple<_column_t, Rhs>;
-				using _table_set = typename ::sqlpp::detail::make_joined_set<typename Lhs::_table_set, typename Rhs::_table_set>::type;
 
 				static_assert(can_be_null_t<_column_t>::value, "column cannot be null");
 
-				assignment_t(_column_t lhs, value_type rhs):
+				assignment_t(_column_t lhs, _value_t rhs):
 					_lhs(lhs), 
 					_rhs(rhs)
 				{}
@@ -135,7 +146,7 @@ namespace sqlpp
 				~assignment_t() = default;
 
 				_column_t _lhs;
-				value_type _rhs;
+				_value_t _rhs;
 			};
 
 		template<typename Context, typename Lhs, typename Rhs>

include/sqlpp11/vendor/concat.h

@@ -40,7 +40,8 @@ namespace sqlpp
 		{
 			static_assert(sizeof...(Args) > 0, "concat requires two arguments at least");
 			static_assert(sqlpp::detail::all_t<is_text_t<First>::value, is_text_t<Args>::value...>::value, "at least one non-text argument detected in concat()");
-			using _table_set = typename ::sqlpp::detail::make_joined_set<typename First::_table_set, typename Args::_table_set...>::type;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename ::sqlpp::detail::make_joined_set<typename First::_required_tables, typename Args::_required_tables...>::type;
 
 			struct _value_type: public First::_value_type::_base_value_type
 			{

include/sqlpp11/vendor/expression.h

@@ -44,7 +44,8 @@ namespace sqlpp
 		{
 			using _value_type = ::sqlpp::detail::boolean;
 			using _parameter_tuple_t = std::tuple<Lhs, Rhs>;
-			using _table_set = typename ::sqlpp::detail::make_joined_set<typename Lhs::_table_set, typename Rhs::_table_set>::type;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Lhs::_required_tables, typename Rhs::_required_tables>::type;
 
 			binary_expression_t(Lhs lhs, Rhs rhs):
 				_lhs(lhs), 
@@ -89,7 +90,8 @@ namespace sqlpp
 		{
 			using _value_type = ::sqlpp::detail::boolean;
 			using _parameter_tuple_t = std::tuple<Lhs, Rhs>;
-			using _table_set = typename ::sqlpp::detail::make_joined_set<typename Lhs::_table_set, typename Rhs::_table_set>::type;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Lhs::_required_tables, typename Rhs::_required_tables>::type;
 
 			binary_expression_t(Lhs lhs, Rhs rhs):
 				_lhs(lhs), 
@@ -134,7 +136,8 @@ namespace sqlpp
 		{
 			using _value_type = ::sqlpp::detail::boolean;
 			using _parameter_tuple_t = std::tuple<Rhs>;
-			using _table_set = typename Rhs::_table_set;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename Rhs::_required_tables;
 
 			unary_expression_t(Rhs rhs):
 				_rhs(rhs)
@@ -171,7 +174,8 @@ namespace sqlpp
 			using _rhs_t = Rhs;
 			using _value_type = typename O::_value_type;
 			using _parameter_tuple_t = std::tuple<_lhs_t, _rhs_t>;
-			using _table_set = typename ::sqlpp::detail::make_joined_set<typename Lhs::_table_set, typename Rhs::_table_set>::type;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Lhs::_required_tables, typename Rhs::_required_tables>::type;
 
 			binary_expression_t(_lhs_t lhs, _rhs_t rhs):
 				_lhs(lhs), 
@@ -209,7 +213,8 @@ namespace sqlpp
 		{
 			using _value_type = typename O::_value_type;
 			using _parameter_tuple_t = std::tuple<Rhs>;
-			using _table_set = typename Rhs::_table_set;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename Rhs::_required_tables;
 
 			unary_expression_t(Rhs rhs):
 				_rhs(rhs)

include/sqlpp11/vendor/extra_tables.h

@@ -47,7 +47,8 @@ namespace sqlpp
 
 				static_assert(::sqlpp::detail::all_t<is_table_t<Tables>::value...>::value, "at least one argument is not a table or join in extra_tables()");
 
-				using _table_set = ::sqlpp::detail::make_joined_set_t<typename Tables::_table_set...>;
+				using _provided_tables = ::sqlpp::detail::make_joined_set_t<typename Tables::_provided_tables...>;
+				using _required_tables = ::sqlpp::detail::make_joined_set_t<typename Tables::_required_tables...>;
 
 
 				extra_tables_t()
@@ -68,7 +69,8 @@ namespace sqlpp
 		struct no_extra_tables_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/from.h

@@ -42,6 +42,8 @@ namespace sqlpp
 			struct from_t
 			{
 				using _is_from = std::true_type;
+				using _required_tables = ::sqlpp::detail::make_joined_set_t<typename Tables::_required_tables...>;
+				using _provided_tables = ::sqlpp::detail::make_joined_set_t<typename Tables::_provided_tables...>;
 				using _is_dynamic = typename std::conditional<std::is_same<Database, void>::value, std::false_type, std::true_type>::type;
 
 				static_assert(_is_dynamic::value or sizeof...(Tables), "at least one table or join argument required in from()");
@@ -51,7 +53,7 @@ namespace sqlpp
 
 				static_assert(::sqlpp::detail::all_t<is_table_t<Tables>::value...>::value, "at least one argument is not a table or join in from()");
 
-				using _table_set = ::sqlpp::detail::make_joined_set_t<typename Tables::_table_set...>;
+				static_assert(_required_tables::size::value == 0, "at least one table depends on another table");
 
 
 				from_t(Tables... tables):
@@ -96,7 +98,8 @@ namespace sqlpp
 		struct no_from_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/group_by.h

@@ -48,7 +48,8 @@ namespace sqlpp
 				using _parameter_tuple_t = std::tuple<Expressions...>;
 				using _parameter_list_t = typename make_parameter_list_t<_parameter_tuple_t>::type;
 
-				using _table_set = typename ::sqlpp::detail::make_joined_set<typename Expressions::_table_set...>::type;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Expressions::_required_tables...>::type;
 
 				static_assert(_is_dynamic::value or sizeof...(Expressions), "at least one expression (e.g. a column) required in group_by()");
 
@@ -106,7 +107,8 @@ namespace sqlpp
 		struct no_group_by_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/having.h

@@ -51,7 +51,8 @@ namespace sqlpp
 
 				using _parameter_list_t = typename make_parameter_list_t<_parameter_tuple_t>::type;
 
-				using _table_set = typename ::sqlpp::detail::make_joined_set<typename Expressions::_table_set...>::type;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Expressions::_required_tables...>::type;
 
 				having_t(Expressions... expressions):
 					_expressions(expressions...)
@@ -102,7 +103,8 @@ namespace sqlpp
 		struct no_having_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/in.h

@@ -56,7 +56,8 @@ namespace sqlpp
 						T in;
 					};
 			};
-			using _table_set = typename ::sqlpp::detail::make_joined_set<typename Operand::_table_set, typename Args::_table_set...>::type;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Operand::_required_tables, typename Args::_required_tables...>::type;
 
 			in_t(Operand operand, Args... args):
 				_operand(operand),

include/sqlpp11/vendor/insert_value.h

@@ -44,7 +44,8 @@ namespace sqlpp
 				struct type_if
 				{
 					using type = Type;
-					using _table_set = typename Type::_table_set;
+					using _provided_tables = detail::type_set<>;
+					using _required_tables = typename Type::_required_tables;
 				};
 
 			template<typename Type>
@@ -52,7 +53,8 @@ namespace sqlpp
 				{
 					struct type
 					{
-						using _table_set = sqlpp::detail::type_set<>;
+						using _provided_tables = detail::type_set<>;
+						using _required_tables = sqlpp::detail::type_set<>;
 					};
 				};
 		}

include/sqlpp11/vendor/insert_value_list.h

@@ -42,7 +42,7 @@ namespace sqlpp
 		// COLUMN AND VALUE LIST
 		struct insert_default_values_t
 		{
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 			using _is_dynamic = std::false_type;
 
 			template<typename Policies>
@@ -69,11 +69,12 @@ namespace sqlpp
 
 					static_assert(sqlpp::detail::none_t<must_not_insert_t<typename Assignments::_column_t>::value...>::value, "at least one assignment is prohibited by its column definition in set()");
 
-				using _column_table_set = typename ::sqlpp::detail::make_joined_set<typename Assignments::_column_t::_table_set...>::type;
+				using _column_required_tables = typename ::sqlpp::detail::make_joined_set<typename Assignments::_column_t::_required_tables...>::type;
-				using _value_table_set = typename ::sqlpp::detail::make_joined_set<typename Assignments::value_type::_table_set...>::type;
+				using _value_required_tables = typename ::sqlpp::detail::make_joined_set<typename Assignments::value_type::_required_tables...>::type;
-				using _table_set = typename ::sqlpp::detail::make_joined_set<_column_table_set, _value_table_set>::type;
+				using _provided_tables = ::sqlpp::detail::type_set<>;
-				static_assert(sizeof...(Assignments) ? (_column_table_set::size::value == 1) : true, "set() contains assignments for tables from several columns");
+				using _required_tables = typename ::sqlpp::detail::make_joined_set<_column_required_tables, _value_required_tables>::type;
-				static_assert(::sqlpp::detail::is_subset_of<_value_table_set, _column_table_set>::value, "set() contains values from foreign tables");
+				static_assert(sizeof...(Assignments) ? (_column_required_tables::size::value == 1) : true, "set() contains assignments for tables from several columns");
+				static_assert(::sqlpp::detail::is_subset_of<_value_required_tables, _column_required_tables>::value, "set() contains values from foreign tables");
 				
 				insert_list_t(Assignments... assignment):
 					_assignments(assignment...),
@@ -203,7 +204,8 @@ namespace sqlpp
 		struct no_insert_value_list_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = ::sqlpp::detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/is_null.h

@@ -39,7 +39,8 @@ namespace sqlpp
 		struct is_null_t: public boolean::template expression_operators<is_null_t<NotInverted, Operand>>
 		{
 			static constexpr bool _inverted = not NotInverted;
-			using _table_set = typename Operand::_table_set;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename Operand::_required_tables;
 
 			struct _value_type: public boolean
 			{

include/sqlpp11/vendor/like.h

@@ -41,7 +41,8 @@ namespace sqlpp
 			static_assert(is_text_t<Operand>::value, "Operand for like() has to be a text");
 			static_assert(is_text_t<Pattern>::value, "Pattern for like() has to be a text");
 			using _parameter_tuple_t = std::tuple<Operand, Pattern>;
-			using _table_set = typename ::sqlpp::detail::make_joined_set<typename Operand::_table_set, typename Pattern::_table_set>::type;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Operand::_required_tables, typename Pattern::_required_tables>::type;
 
 			struct _value_type: public boolean
 			{

include/sqlpp11/vendor/limit.h

@@ -42,7 +42,8 @@ namespace sqlpp
 				using _is_limit = std::true_type;
 				static_assert(is_integral_t<Limit>::value, "limit requires an integral value or integral parameter");
 				// FIXME: Is this really always empty?
-				using _table_set = ::sqlpp::detail::type_set<>;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = ::sqlpp::detail::type_set<>;
 
 				limit_t(Limit value):
 					_value(value)
@@ -67,7 +68,8 @@ namespace sqlpp
 			{
 				using _is_limit = std::true_type;
 				using _is_dynamic = std::true_type;
-				using _table_set = ::sqlpp::detail::type_set<>;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = ::sqlpp::detail::type_set<>;
 
 				dynamic_limit_t():
 					_value(noop())
@@ -107,7 +109,8 @@ namespace sqlpp
 		struct no_limit_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/offset.h

@@ -40,7 +40,8 @@ namespace sqlpp
 			struct offset_t
 			{
 				using _is_offset = std::true_type;
-				using _table_set = ::sqlpp::detail::type_set<>;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = ::sqlpp::detail::type_set<>;
 				static_assert(is_integral_t<Offset>::value, "offset requires an integral value or integral parameter");
 
 				offset_t(Offset value):
@@ -66,7 +67,8 @@ namespace sqlpp
 			{
 				using _is_offset = std::true_type;
 				using _is_dynamic = std::true_type;
-				using _table_set = ::sqlpp::detail::type_set<>;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = ::sqlpp::detail::type_set<>;
 
 				dynamic_offset_t():
 					_value(noop())
@@ -106,7 +108,8 @@ namespace sqlpp
 		struct no_offset_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/order_by.h

@@ -47,7 +47,8 @@ namespace sqlpp
 				using _parameter_tuple_t = std::tuple<Expressions...>;
 				using _parameter_list_t = typename make_parameter_list_t<_parameter_tuple_t>::type;
 
-				using _table_set = typename ::sqlpp::detail::make_joined_set<typename Expressions::_table_set...>::type;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Expressions::_required_tables...>::type;
 
 				static_assert(_is_dynamic::value or sizeof...(Expressions), "at least one sort-order expression required in order_by()");
 
@@ -104,7 +105,8 @@ namespace sqlpp
 		struct no_order_by_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/select_column_list.h

@@ -137,7 +137,8 @@ namespace sqlpp
 				using _parameter_tuple_t = std::tuple<Columns...>;
 				using size = std::tuple_size<_parameter_tuple_t>;
 
-				using _table_set = sqlpp::detail::make_joined_set_t<typename Columns::_table_set...>;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = sqlpp::detail::make_joined_set_t<typename Columns::_required_tables...>;
 
 				static_assert(not ::sqlpp::detail::has_duplicates<Columns...>::value, "at least one duplicate argument detected");
 
@@ -245,7 +246,8 @@ namespace sqlpp
 		struct no_select_column_list_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 			template<typename Db>
 				using _result_row_t = ::sqlpp::result_row_t<Db>;
 			using _dynamic_names_t = typename dynamic_select_column_list<void>::_names_t;

include/sqlpp11/vendor/select_flag_list.h

@@ -46,7 +46,8 @@ namespace sqlpp
 				using _is_dynamic = typename std::conditional<std::is_same<Database, void>::value, std::false_type, std::true_type>::type;
 				using _parameter_tuple_t = std::tuple<Flags...>;
 				using size = std::tuple_size<_parameter_tuple_t>;
-				using _table_set = typename ::sqlpp::detail::make_joined_set<typename Flags::_table_set...>::type;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Flags::_required_tables...>::type;
 
 				static_assert(not ::sqlpp::detail::has_duplicates<Flags...>::value, "at least one duplicate argument detected in select flag list");
 
@@ -102,7 +103,8 @@ namespace sqlpp
 		struct no_select_flag_list_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/single_table.h

@@ -39,8 +39,11 @@ namespace sqlpp
 			struct single_table_t
 			{
 				using _is_single_table = std::true_type;
+				using _required_tables = typename Table::_required_tables;
+				using _provided_tables = typename Table::_provided_tables;
 
 				static_assert(is_table_t<Table>::value, "argument has to be a table");
+				static_assert(_required_tables::size::value == 0, "table depends on another table");
 
 				single_table_t(Table table):
 					_table(table)
@@ -52,13 +55,13 @@ namespace sqlpp
 				single_table_t& operator=(single_table_t&&) = default;
 				~single_table_t() = default;
 
-				using _table_set = typename Table::_table_set;
 				Table _table;
 			};
 
 		struct no_single_table_t
 		{
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 		};
 
 		// Interpreters

include/sqlpp11/vendor/update_list.h

@@ -112,7 +112,8 @@ namespace sqlpp
 		struct no_update_list_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/using.h

@@ -51,7 +51,8 @@ namespace sqlpp
 
 				static_assert(::sqlpp::detail::all_t<is_table_t<Tables>::value...>::value, "at least one argument is not an table in using()");
 
-				using _table_set = ::sqlpp::detail::make_joined_set_t<typename Tables::_table_set...>;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = ::sqlpp::detail::make_joined_set_t<typename Tables::_required_tables...>;
 
 				using_t(Tables... tables):
 					_tables(tables...)
@@ -96,7 +97,8 @@ namespace sqlpp
 		struct no_using_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/where.h

@@ -52,7 +52,8 @@ namespace sqlpp
 
 				using _parameter_list_t = typename make_parameter_list_t<_parameter_tuple_t>::type;
 
-				using _table_set = typename ::sqlpp::detail::make_joined_set<typename Expressions::_table_set...>::type;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = typename ::sqlpp::detail::make_joined_set<typename Expressions::_required_tables...>::type;
 
 				where_t(Expressions... expressions):
 					_expressions(expressions...)
@@ -105,7 +106,8 @@ namespace sqlpp
 			{
 				using _is_where = std::true_type;
 				using _is_dynamic = std::false_type;
-				using _table_set = ::sqlpp::detail::type_set<>;
+				using _provided_tables = detail::type_set<>;
+				using _required_tables = ::sqlpp::detail::type_set<>;
 
 				where_t(bool condition):
 					_condition(condition)
@@ -128,7 +130,8 @@ namespace sqlpp
 		struct no_where_t
 		{
 			using _is_noop = std::true_type;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			template<typename Policies>
 				struct _methods_t

include/sqlpp11/vendor/wrap_operand.h

@@ -48,7 +48,8 @@ namespace sqlpp
 			static constexpr bool _is_expression = true;
 			using _value_type = sqlpp::detail::boolean;
 			using _value_t = bool;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			boolean_operand():
 				_t{}
@@ -86,7 +87,8 @@ namespace sqlpp
 			static constexpr bool _is_expression = true;
 			using _value_type = ::sqlpp::detail::integral;
 			using _value_t = int64_t;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			integral_operand():
 				_t{}
@@ -125,7 +127,8 @@ namespace sqlpp
 			static constexpr bool _is_expression = true;
 			using _value_type = ::sqlpp::detail::floating_point;
 			using _value_t = double;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			floating_point_operand():
 				_t{}
@@ -163,7 +166,8 @@ namespace sqlpp
 			static constexpr bool _is_expression = true;
 			using _value_type = ::sqlpp::detail::text;
 			using _value_t = std::string;
-			using _table_set = ::sqlpp::detail::type_set<>;
+			using _provided_tables = detail::type_set<>;
+			using _required_tables = ::sqlpp::detail::type_set<>;
 
 			text_operand():
 				_t{}

include/sqlpp11/verbatim_table.h

@@ -49,8 +49,6 @@ namespace sqlpp
 
 	struct verbatim_table_t: public sqlpp::table_t<verbatim_table_t, detail::unusable_pseudo_column_t>
 	{
-		using _value_type = no_value_t;
-
 		verbatim_table_t(std::string name):
 			_name(name)
 		{