has many fetch with join

backends/postgres/include/postgres_result_reader.hpp

@@ -44,6 +44,7 @@ public:
   [[nodiscard]] const char *column(size_t index) const override;
   utils::result<bool, utils::error> fetch() override;
   [[nodiscard]] size_t start_column_index() const override;
+  void unshift() override;
 
   void read_value(const char *id, size_t index, int8_t &value) override;
   void read_value(const char *id, size_t index, int16_t &value) override;

backends/postgres/src/postgres_result_reader.cpp

@@ -34,6 +34,12 @@ size_t postgres_result_reader::start_column_index() const {
   return 0;
 }
 
+void postgres_result_reader::unshift() {
+  if (row_index_ > 0) {
+    --row_index_;
+  }
+}
+
 void postgres_result_reader::read_value(const char * /*id*/, const size_t index, int8_t &value) {
   if (auto res = utils::to<int8_t>(column(index)); res.is_ok()) {
     value = res.value();