added timestamp code, support columns for group by and order by and tested load has-many eager code

test/backends/QueryRecordTest.cpp

@@ -120,7 +120,6 @@ TEST_CASE_METHOD(QueryFixture, "Test all data types for record", "[query][record
   REQUIRE(str == row.at<std::string>("val_string"));
   REQUIRE(varchar == row.at<std::string>("val_varchar"));
   REQUIRE(md == row.at<date_type_t>("val_date"));
-  const auto mtres = row.at<time_type_t>("val_time");
   REQUIRE(mt == row.at<time_type_t>("val_time"));
   REQUIRE(bin == row.at<blob_type_t>("val_blob"));
 }
@@ -510,7 +509,7 @@ TEST_CASE_METHOD(QueryFixture, "Execute select statement with group by and order
 
   auto result = query::select({count("age").as("age_count"), "age"})
     .from("person")
-    .group_by("age")
+    .group_by({"age"})
     .order_by("age_count").desc()
     .fetch_all(db);
   REQUIRE(result.is_ok());