var total = (from a in all

                             join g in group_M                                        on new { MetricPointID = a.MetricPointID, UsageDate = a.UsageDate }                                        equals new { MetricPointID = g.MetricPointID, UsageDate = g.MaxUsageDate }                              select new                              {                                  MetricPointID = a.MetricPointID,                                  TotalMonth = a.TotalMonth,                                  TotalYear = a.TotalYear,                                  AlertTotalMonth = a.AlertTotalMonth,                                  AlertTotalYear = a.AlertTotalYear,                              }).ToList();

 

多条件就使用匿名类