query preparations for std::optional

include/matador/sql/column.hpp

@@ -130,10 +130,10 @@ private:
  */
 column operator "" _col(const char *name, size_t len);
 
-column make_column(const std::string &name, data_type_t type, utils::field_attributes attr = utils::null_attributes);
+column make_column(const std::string &name, data_type_t type, utils::field_attributes attr = utils::not_null_attributes);
 
 template < typename Type >
-column make_column(const std::string &name, utils::field_attributes attr = utils::null_attributes)
+column make_column(const std::string &name, utils::field_attributes attr = utils::not_null_attributes)
 {
     return make_column(name, data_type_traits<Type>::builtin_type(0), attr);
 }

include/matador/utils/field_attributes.hpp

@@ -30,6 +30,7 @@ private:
 };
 
 const field_attributes null_attributes {};
+const field_attributes not_null_attributes { constraints::NOT_NULL };
 
 }
 #endif //QUERY_FIELD_ATTRIBUTES_HPP