Query: SQL group by when aggregate operators have complex expression

[smitpatel]

        [ConditionalFact]
        public virtual void GroupBy_Property_Select_Sum()
        {
            AssertQueryScalar<Order>(os => os.GroupBy(o => o.CustomerID).Select(g => g.Sum(o => o.OrderID + 5)));
        }

Is client evaluated since the expression inside Sum is not member expression. That is our current logic to avoid issues with unmapped properties. In general we can relax the criteria but currently we decide in RequiresMaterialization if we can translate of not. At that point we cannot accurately know if we can translate it or not. (materialization tells client group by vs server group by). We can remove strict check and allow translation of more patterns but if something which cannot be translated is encountered then we fail.

As an effective fix for this (and other issue with joins #10012 ) we can pull the selector into GroupResultOperator (with custom operator) and we can make determination of group by during translation strictly.

[smitpatel]

Dependent on #12089