var query3 = from eItems in resTab.AsEnumerable()
                         join eItems2 in TempTab.AsEnumerable()
                         on eItems.Field<string>("id_порода") equals
                            eItems2.Field<string>("id_порода")
                         group eItems by new
                         {
                             Por = eItems.Field<string>("id_порода"),
                             Temp = eItems2.Field<string>("Temp"),
                         } into grouping
                         select new
                         {
                             porID =
                                 grouping.Key,
                             SumCount =
                                 grouping.Key.Temp,
                             MaxCount =
                                 grouping.Max(eItems => Convert.ToInt16(eItems.Field<string>("Count")))
                         };

                        (SELECT t3.por, t3.CountN, t3.SumM, t4.MaxR FROM
			(SELECT t1.por, CountN, SumM FROM
			(SELECT por, count(N) as CountN FROM tab1 GROUP BY por) t1
			LEFT JOIN 
			(SELECT por, Sum(M) as SumM FROM tab2 GROUP BY por) t2
			ON t1.por = t2.por) t3
			LEFT JOIN 
			(SELECT por, Max(R) as MaxR FROM tab3 GROUP BY por) t4
			ON t3.por = t4.por