Introduced unary function templates which use one pair of braces less

This is required for sqlite which cannot parse

SELECT EXISTS((SELECT 1))

include/sqlpp11/expression.h

@@ -315,6 +315,38 @@ namespace sqlpp
 			std::tuple<Rhs...> _rhs;
 		};
 
+	template<typename F, typename Rhs>
+		struct unary_function_t: public F::_value_type::template operators<unary_function_t<F, Rhs>>
+		{
+			using _value_type = typename F::_value_type;
+
+			unary_function_t(Rhs&& r):
+				_rhs(std::move(r))
+			{}
+
+			unary_function_t(const Rhs& r):
+				_rhs(r)
+			{}
+
+			unary_function_t(const unary_function_t&) = default;
+			unary_function_t(unary_function_t&&) = default;
+			unary_function_t& operator=(const unary_function_t&) = default;
+			unary_function_t& operator=(unary_function_t&&) = default;
+			~unary_function_t() = default;
+
+			template<typename Db>
+				void serialize(std::ostream& os, Db& db) const
+				{
+					os << F::_name;
+					os << "(";
+					_rhs.serialize(os, db);
+					os << ")";
+				}
+
+		private:
+			Rhs _rhs;
+		};
+
 	template<typename F, typename... Rhs>
 		struct named_nary_function_t: public F::_value_type::template operators<named_nary_function_t<F, Rhs...>>
 		{
@@ -347,6 +379,39 @@ namespace sqlpp
 		private:
 			std::tuple<Rhs...> _rhs;
 		};
+
+	template<typename F, typename Rhs>
+		struct named_unary_function_t: public F::_value_type::template operators<named_unary_function_t<F, Rhs>>
+		{
+			using _value_type = typename F::_value_type;
+			using _name_t = typename F::_name_t;
+
+			named_unary_function_t(Rhs&& r):
+				_rhs(std::move(r))
+			{}
+
+			named_unary_function_t(const Rhs& r):
+				_rhs(r)
+			{}
+
+			named_unary_function_t(const named_unary_function_t&) = default;
+			named_unary_function_t(named_unary_function_t&&) = default;
+			named_unary_function_t& operator=(const named_unary_function_t&) = default;
+			named_unary_function_t& operator=(named_unary_function_t&&) = default;
+			~named_unary_function_t() = default;
+
+			template<typename Db>
+				void serialize(std::ostream& os, Db& db) const
+				{
+					os << F::_name_t::_get_name();
+					os << "(";
+					_rhs.serialize(os, db);
+					os << ")";
+				}
+
+		private:
+			Rhs _rhs;
+		};
 }
 
 #endif

include/sqlpp11/functions.h

@@ -60,7 +60,7 @@ namespace sqlpp
 					};\
 				};\
 				\
-				using type = named_nary_function_t<_op, _operand>;\
+				using type = named_unary_function_t<_op, _operand>;\
 			};\
 	}\
 	template<typename T>\