int sum = behzad.Compare_closed_numbers_in_CRM_and_Billing_system_detail_counters
.Where(t=>t.fileid == point.id)
.Select(t => t.Count ?? 0).Sum();
nvarchar(max)
,请尝试以下方法:int sum = behzad.Compare_closed_numbers_in_CRM_and_Billing_system_detail_counters
.Where(t=>t.fileid == point.id)
.Select(t => Convert.ToInt32(t.Count)).Sum();