Question

我有这个SQL查询，我需要转换为LINQ：

SELECT * 
FROM USER U
INNER JOIN (
    SELECT USERID , MAX(SALESDATE) AS MAXDATE
    FROM SALES
    GROUP BY USERID) S ON U.ID = S.USERID

到目前为止，这就是我提出的LINQ：

var Users = (from d in db.Users
             join s in db.Sales on d.Id equals s.UserId
             select new Models.User
             {
                Id = d.Id,
                UserName = d.UserName,
                FirstName = d.FirstName,
                LastName = d.LastName,
                EmailAddress = d.EmailAddress,
                PhoneNumber = d.PhoneNumber,
                LastPurchase = s.SalesDate
             }).Max(x => x.SalesDate);

但是，我很确定结果不一样。任何人都可以建议将其转换为LINQ的正确方法吗？我还是学习LINQ的新手。我非常感谢你的帮助。

Answer 1

试试这个

var Users = (from d in db.Users
             from s in db.Sales.where(x=>x.Userid==d.id).groupby(x=>x.Userid)
             select new Models.User
             {
                Id = d.Id,
                UserName = d.UserName,
                FirstName = d.FirstName,
                LastName = d.LastName,
                EmailAddress = d.EmailAddress,
                PhoneNumber = d.PhoneNumber,
                LastPurchase = s.Max(x=>x.SalesDate)
             }).ToList();

Answer 2

您当前的Linq查询，首先加入整个表，然后选择与您在Sales表中首先选择的SQL结果相反，然后加入该结果（示例中的别名S ）。

var query = from u in db.Users
            join s in (from sale in db.Sales
                       group sale by sale.Id into grp
                       select new {
                           Id = grp.Key,
                           LastPurchase = grp.Max(item => item.SalesDate)
                       })
            on u.Id equals s.Id
            select /* what you need to retrieve */;

Answer 3

你可以这样做：

        var query1 = from sale in db.Sales
                     group sale by sale.UserId into g
                     let maxDate = g.Max(s => s.SalesDate)
                     select new { UserId = g.Key, maxDate };

        var query2 = from user in db.Users
                     from q1 in query1.Where(q => q.UserId == user.Id)
                     select new { user.Id, user.UserName, user.Firstname, user.lastname, ... , q1.maxDate };

        var result = query2.ToList();

LINQ中SQL的Max函数等价于什么？

3 个答案: