fixed nextval and update tests

source/orm/query/intermediates/query_select_intermediate.cpp

@@ -12,6 +12,7 @@ query_select_intermediate::query_select_intermediate(const std::vector<table_col
 }
 
 fetchable_query query_select_intermediate::nextval(const std::string& sequence_name) {
+  context_->parts.pop_back();
   context_->parts.push_back(std::make_unique<internal::query_select_nextval_part>(sequence_name));
   return {context_};
 }

source/orm/query/query_builder.cpp

@@ -100,7 +100,7 @@ void query_builder::visit(internal::query_select_part &part) {
 }
 
 void query_builder::visit(internal::query_select_nextval_part& part) {
-  query_.sql += dialect_->nextval() + "('" + part.sequence_name() + "')";
+  query_.sql += dialect_->select() + " " + dialect_->nextval() + "('" + part.sequence_name() + "')";
   prepare_prototype(query_.prototype, part.sequence_name());
 }