Linq 中的 SQL：每列的组和最大值

Question

我要把这条 SQL 语句转换成 Linq：

select id, workerId, max(timestamp) as Datex, clientId from order where clientId = '123' group by workerId;

它使用表格顺序的每一列创建一个表格。但它只显示 clientID=123 的行并按工人分组。它只显示最新条目（最大时间戳）

如何将其传输到 Linq？我什么都试过了。例如，这不起作用：

var selectedOrder = from s in order
                    where s.clientID == "123"
                    group s by s.workerId into g
                    select new {  id = s.id, workerId = g.Key, Datex = g.Max(s => s.timestamp), s.clientID};

更新：

1. 我想给你举个例子：

id: 1   workerId: 162   Datex: 2014-11-13   clientId: 123 
id: 2   workerId: 162   Datex: 2016-01-07   clientId: 123 
id: 3   workerId: 222   Datex: 2015-12-12   clientId: 123 
id: 4   workerId: 222   Datex: 2013-01-22   clientId: 100 
id: 2   workerId: 162   Datex: 2011-11-07   clientId: 123

由于我想要的查询：

  id: 2   workerId: 162   Datex: 2016-01-07   clientId: 123 
  id: 3   workerId: 222   Datex: 2015-12-12   clientId: 123

--> 所以我的第一张桌子上只有两个不同的工人。我想为每个工人显示最新日期的行

Answer 1

你可以使用OrderBy和First()，查询应该是这样的

var selectedOrder = (from s in order
            where s.clientID == "123"
            select new
            {
                id = s.id,
                workerId = s.workerId,
                Datex = s.timestamp,
                clientID =s.clientID
            }).OrderBy(d => d.Datex).First();

或GroupBy 多列

var selectedOrder = from s in order
            where s.clientID == "123"
            group s by new {s.workerId, s.id, s.clientID}
            into g
            select
            new
            {
                id = g.Key.id,
                workerId = g.Key.workerId,
                Datex = g.Max(s => s.timestamp),
                clientID = g.Key.clientID
            };