How do I group and group two tables together?

Is there an error? Just nothing returning?

Thank you Trevor

I Solved

Code Samples

var CategoryAndProductCustomColumuns2 = CustomTableItemProvider.GetItems("customtable.MyJoinCategory").Source(s => s.LeftJoin("customtable_MyJoinProduct", "ItemID", "CategoryID")).Column("Name").AddColumn(new CountColumn("CategoryID").As("ProductCount")).GroupBy("CategoryID,Name").Result;