linq to datatable 和lambda查询datatable

用Linq查询DataTable

        static DataTable table = new DataTable();
        static DataColumn dc = new DataColumn();
        static void Main()
        {
            Createtable();
            table.Rows.Add(, ,"2010-1-1");
            table.Rows.Add(, , "2010-1-1");
            table.Rows.Add(, , "2010-1-1");
            table.Rows.Add(, , "2010-1-1");
            table.Rows.Add(, , "2010-1-2");
            table.Rows.Add(, , "2010-1-2");
            table.Rows.Add(, , "2010-1-2");
            table.Rows.Add(, , "2010-1-2");
 
            var query = from dt in table.AsEnumerable()
                        where new int[] { , ,  }.Contains(dt.Field<Int32>("PID"))
                        orderby dt.Field<DateTime>("CreateDate") descending
                        group dt by dt.Field<Int32>("PID") into g
                        let n = (from d in g.Take().Skip() select d).FirstOrDefault()
                        select new
                        {
                            ID = n.Field<Int32>("ID"),
                            PID = g.Key,
                            CreateDate = n.Field<DateTime>("CreateDate")
                        };
            query.ToList().ForEach(m => Console.WriteLine("{0}\t{1}\t{2}\t",m.ID,m.PID,m.CreateDate));
        }
        public static void Createtable()
        {
            dc = new DataColumn("ID", Type.GetType("System.Int32"));
            table.Columns.Add(dc);
            dc = new DataColumn("PID", Type.GetType("System.Int32"));
            table.Columns.Add(dc);
            dc = new DataColumn("CreateDate", Type.GetType("System.DateTime"));
            table.Columns.Add(dc);
        }

用Lambda表达式查询DataTable

DataTable dt = new DataTable();
            DataColumn dc = new DataColumn("UserName", System.Type.GetType("System.String"));
            DataColumn dc1 = new DataColumn("UserPwd", System.Type.GetType("System.String"));
            dt.Columns.Add(dc);
            dt.Columns.Add(dc1);
            DataRow dr = dt.NewRow();
            dr["UserName"] = "";
            dr["UserPwd"] = "";
            dt.Rows.Add(dr);
 
            var rownumber = dt.AsEnumerable().Where<DataRow>(C=>C["UserName"].ToString()=="");
            int row = rownumber.Count<DataRow>();
            foreach ( DataRow en in  rownumber)
            {
 
                Response.Write("User" + en["UserName"] + "pwd" + en["UserPwd"]);
            }