Linq中如何取出每个用户的符合条件的第一条记录？

百思软件工作室 2010-10-25 06:13:04

Linq中如何取出每个用户的符合条件的第一条记录？

数据库有以下几个字段：
主键用户id 名次时间是否正常
1 100 10 20101012 1
2 100 20 20101009 1
3 200 11 20101011 1
4 100 18 20101008 1
5 300 2 20101010 1
6 300 15 20101013 1
7 300 16 20101002 0
我要得到这样的结果：
100 18 20101008
200 11 20101011
300 2 20101010
请问这个用Linq怎么实现？？

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keke811 2011-08-26

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sp1234
在灌水.

sanba1100 2010-10-30

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linq是什么？？

以专业开发人员为伍 2010-10-30

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入门学linq看这里：http://msdn.microsoft.com/en-us/vcsharp/aa336746.aspx

caoshuming_500 2010-10-30

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学习了先分组后按时间排序

Cobra_520 2010-10-29

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我也有点犯晕来看看

百思软件工作室 2010-10-28

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var userobj = (
from a in dc.TradeKey
where a.Status == 0 && a.Level.Trim() == Level && a.StartTime.HasValue
group a by a.UserID into g
select new iTry86.UserLib.Model.TradeKey
{
UserID = g.Key,
SN = g.OrderByDescending(t => t.StartTime).Select(t => t.SN).First()
}
)
.ToArray();
用Linq搞定了，谢谢楼上的指导
如果这个用SQL
select top 1 userid,keyid from A group by userid
怎么不行啊？

flyerwing 2010-10-26

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XXX类型 en=lst.First();
好象成吧.

PxxxP 2010-10-26

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 public class User { public string UserId { get; set; } public string Rank { get; set; } public string Date { get; set; } public string IsNormal { get; set; } }

       



 static IEnumerable<User> GetData()

        {

            yield return new User { UserId = "100", Rank = "10", Date = "20101012", IsNormal = "1" };

            yield return new User { UserId = "100", Rank = "20", Date = "20101009", IsNormal = "1" };

            yield return new User { UserId = "200", Rank = "11", Date = "20101011", IsNormal = "1" };

            yield return new User { UserId = "100", Rank = "18", Date = "20101008", IsNormal = "1" };

            yield return new User { UserId = "300", Rank = "2", Date = "20101010", IsNormal = "1" };

            yield return new User { UserId = "300", Rank = "15", Date = "20101013", IsNormal = "1" };

            yield return new User { UserId = "300", Rank = "16", Date = "20101002", IsNormal = "0" };

        }



        static void Main(string[] args)

        {



            var Query = from user in GetData()

                        where user.IsNormal=="1"

                        group user by user.UserId into g

                        select new { 

                            UserId = g.Key, 

                            Rank = (GetData().Where(d => d.Date == g.Min(u => u.Date)).Select(d=>d.Rank)).First(), 

                            Date = g.Min(u => u.Date) };

            foreach (var v in Query)

            {

                Console.WriteLine("UserID={0}      Rank={1}       Date={2}",v.UserId,v.Rank,v.Date);

            }



            /*

            UserID=100      Rank=18       Date=20101008

            UserID=200      Rank=11       Date=20101011

            UserID=300      Rank=2       Date=20101010

            */

光脚丫思考 2010-10-26

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使用Where()和First()运算符的组合运算，在Where()运算符中指定查询条件。第二种做法就是只使用First()运算符，将查询条件作为参数传递给此方法。有疑问，继续留言！

机器人 2010-10-25

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还少个User的类定义。



    public class User

    {

        public string UserId { get; set; }

        public string Rank { get; set; }

        public string Date { get; set; }

        public string IsNormal { get; set; }

    }

机器人 2010-10-25

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  static void Main(string[] args)

        {

            var list = GetData();



            var query =

                    from u in list

                    where u.IsNormal == "1"

                    group u by u.UserId into g

                    orderby g.Key

                    from u2 in g

                    where u2.Date == g.Min(u3 => u3.Date)

                    select u2;



            foreach (var u in query)

                Console.WriteLine("{0}, {1}, {2}", u.UserId, u.Date, u.Rank);

            



            Console.Read();

        }



        static IEnumerable<User> GetData()

        {

            yield return new User { UserId = "100", Rank = "10", Date = "20101012", IsNormal = "1" };

            yield return new User { UserId = "100", Rank = "20", Date = "20101009", IsNormal = "1" };

            yield return new User { UserId = "200", Rank = "11", Date = "20101011", IsNormal = "1" };

            yield return new User { UserId = "100", Rank = "18", Date = "20101008", IsNormal = "1" };

            yield return new User { UserId = "300", Rank = "2", Date = "20101010", IsNormal = "1" };

            yield return new User { UserId = "300", Rank = "15", Date = "20101013", IsNormal = "1" };

            yield return new User { UserId = "300", Rank = "16", Date = "20101002", IsNormal = "0" };

        }