Question

我有一个表审核登录，我想为每个用户提取最新的登录信息，以下sql完成。

如何将sql查询格式化为linq to sql查询？

SELECT * FROM AuditTable adt1
    inner join UserTable usr
        on adt1.[UserName] = usr.[User_Id]
WHERE [TimeStamp] = ( SELECT MAX([TimeStamp])
                      FROM AuditTable adt2
                      WHERE adt1.UserName = adt2.UserName)

在sql中编写查询的另一种方法是;

SELECT adt1.[UserName], usr.First_Name, max([TimeStamp]) as [TimeStamp]
FROM AuditTable adt1
    INNER JOIN UserTable usr
        on adt1.[UserName] = usr.[User_Id]
GROUP BY adt1.[UserName] ,usr.First_Name

Answer 1

查询＃2：
来自ad.1 in dc.AuditTable
在adt1.UserName == usr.UserID上加入dc.UserTable中的usr group adt1 by adt1.username int ag
选择新{UserName = ag.Key，TSMax = ag.Max（ts =＆gt; adt1.TimeStamp）}

为什么要加入用户表？过滤

Answer 2

我开始工作......答案是使用let关键字。

另外，我强烈建议您在尝试解决这些问题时使用LinqPad。

from adt in AuditTable
    join usr in UserTable
        on adt.UserName equals usr.User_Id
group adt by 
    new { adt.UserName, adt.Roles, usr.First_Name, usr.Last_Name } 
into g
let LastAccessed = g.Max(a => a.TimeStamp)
select new 
    { UserName = g.Key.UserName,
      Roles = g.Key.Roles,
      FirstName = g.Key.First_Name,
      LastName = g.Key.Last_Name,
      TimeStamp = LastAccessed
    }

将group by子句和/或聚合函数的Sql查询转换为linq到sql？

2 个答案: