最近项目有一个需求，从订单表查询出每个客户最近一条订单记录。数据库表结构如下图
SELECT * FROM (
select ROW_NUMBER()over(partition by [custid] order by [orderdate] desc) AS newIndex,* from Sales.Orders
) as T where T.newIndex=1
执行结果，已经按照客户分组，并且按时间顺序生成序号。
对应LINQ代码为
var table = contex.GetTable<Orders>().ToList();
var data = table.OrderByDescending(a => a.orderdate).GroupBy(a => a.custid)
.Select(g => new { g, count = g.Count() })
.SelectMany(t => t.g.Select(b => b)
.Zip(Enumerable.Range(, t.count), (j, i) => new { j.custid, j.shipname, rn = i }));