使用Linq group by 查询 一般我们都会这样写Linq：

var result = (from si in model.table
group si by si.NumCores into grp orderby grp.Key
select new CoreCount { Cores = grp.Key, Count = grp.Count() }).ToList();

正确的答案（MySql）：

var result = (from si in model.table
group si by si.NumCores into grp orderby grp.Key
select new CoreCount { Cores = grp.FirstOrDefault().NumCores, Count = grp.Count() }).ToList();


以上在MySQL亲测有效，SQL server没有测试。。。

C# linq group by 异常 -----MySqlException: Unknown column 'GroupBy1.K1' in 'field list'