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