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我只是想知道如果任何人都可以提供任何建議，以改善我的查詢。LINQ到SQL - 慢查詢
基本上，它會將2行合併到1中。唯一不同的行是'類型'字符列（'S'或'C'）和值。我想要做的是用'S'值和'C'值選擇一行，並計算差值（S-C）。
我的查詢很有用，但速度很慢 - 大約需要8秒才能得到結果，這對我的應用程序來說並不理想。我希望我可以改變數據庫結構，但我不能傷心！
這裏是我的查詢：
var sales = (from cm in dc.ConsignmentMarginBreakdowns
join sl in dc.SageAccounts on new { LegacyID = cm.Customer, Customer = true } equals new { LegacyID = sl.LegacyID, Customer = sl.Customer }
join ss in dc.SageAccounts on sl.ParentAccount equals ss.ID
join vt in dc.VehicleTypes on cm.ConsignmentTripBreakdown.VehicleType.Trim() equals vt.ID.ToString() into vtg
where cm.ConsignmentTripBreakdown.DeliveryDate >= dates.FromDate && cm.ConsignmentTripBreakdown.DeliveryDate <= dates.ToDate
where (customer == null || ss.SageID == customer)
where cm.BreakdownType == 'S'
orderby cm.Depot, cm.TripNumber
select new
{
NTConsignment = cm.NTConsignment,
Trip = cm.ConsignmentTripBreakdown,
LegacyID = cm.LegacyID,
Costs = dc.ConsignmentMarginBreakdowns.Where(a => a.BreakdownType == 'C' && a.NTConsignment == cm.NTConsignment && a.LegacyID == cm.LegacyID && a.TripDate == cm.TripDate && a.Depot == cm.Depot && a.TripNumber == cm.TripNumber).Single().Value,
Sales = cm.Value ?? 0.00m,
Customer = cm.Customer,
SageID = ss.SageID,
CustomerName = ss.ShortName,
FullCustomerName = ss.Name,
Vehicle = cm.ConsignmentTripBreakdown.Vehicle ?? "None",
VehicleType = vtg.FirstOrDefault().VehicleTypeDescription ?? "Subcontractor"
});