AVG, SUM, MAX, MIN Overload

Src/Asp.Net/SqlServerTest/Demos/1_Query.cs

@@ -162,6 +162,7 @@ namespace OrmTest.Demo
             var getByWhere = db.Queryable<Student>().Where(it => it.Id == 1 || it.Name == "a").ToList();
             var getByFuns = db.Queryable<Student>().Where(it => SqlFunc.IsNullOrEmpty(it.Name)).ToList();
             var sum = db.Queryable<Student>().Sum(it => it.Id);
+            var sum2 = db.Queryable<Student,School>((st,sc)=>st.SchoolId==sc.Id).Sum((st,sc) => sc.Id);
             var isAny = db.Queryable<Student>().Where(it => it.Id == -1).Any();
             var isAny2 = db.Queryable<Student>().Any(it => it.Id == -1);
             var getListByRename = db.Queryable<School>().AS("Student").ToList();