优化linq到sql查询

我有一个非常繁重的LINQ-to-SQL查询，它在不同的表上执行许多连接以返回一个匿名类型。问题是，如果返回的行数相当大(> 200)，那么查询就会变得非常慢，最终会超时。我知道我可以增加数据上下文超时设置，但这是最后的手段。

我只是想知道如果我把它分开，我的查询是否会更好地工作，并把我的比较作为linq到对象的查询，所以我甚至可以使用PLINQ来最大化处理能力。但这对我来说是一个陌生的概念，我不知道该怎么把它分开。谁能给点建议?我并不是要求别人帮我写代码，只是一些关于我如何改进的一般性指导，这将是伟大的。

注意，我已经确保数据库中有我所加入的所有正确的键，并且我已经确保这些键是最新的。

查询如下:

var cons = (from c in dc.Consignments
            join p in dc.PODs on c.IntConNo equals p.Consignment into pg
            join d in dc.Depots on c.DeliveryDepot equals d.Letter
            join sl in dc.Accounts on c.Customer equals sl.LegacyID
            join ss in dc.Accounts on sl.InvoiceAccount equals ss.LegacyID
            join su in dc.Accounts on c.Subcontractor equals su.Name into sug
            join sub in dc.Accountsubbies on ss.ID equals sub.AccountID into subg
            where (sug.FirstOrDefault() == null
                || sug.FirstOrDefault().Customer == false)
            select new
            {
                 ID = c.ID,
                 IntConNo = c.IntConNo,
                 LegacyID = c.LegacyID,
                 PODs = pg.DefaultIfEmpty(),
                 TripNumber = c.TripNumber,
                 DropSequence = c.DropSequence,
                 TripDate = c.TripDate,
                 Depot = d.Name,
                 CustomerName = c.Customer,
                 CustomerReference = c.CustomerReference,
                 DeliveryName = c.DeliveryName,
                 DeliveryTown = c.DeliveryTown,
                 DeliveryPostcode = c.DeliveryPostcode,
                 VehicleText = c.VehicleReg + c.Subcontractor,
                 SubbieID = sug.DefaultIfEmpty().FirstOrDefault().ID.ToString(),
                 SubbieList = subg.DefaultIfEmpty(),
                 ScanType = ss.PODScanning == null ? 0 : ss.PODScanning
            });

下面是根据请求生成的SQL:

    {SELECT [t0].[ID], [t0].[IntConNo], [t0].[LegacyID], [t6].[test], [t6].[ID] AS [ID2], [t6].[Consignment], [t6].[Status], [t6].[NTConsignment], [t6].[CustomerRef], [t6].[Timestamp], [t6].[SignedBy], [t6].[Clause], [t6].[BarcodeNumber], [t6].[MainRef], [t6].[Notes], [t6].[ConsignmentRef], [t6].[PODedBy], (
    SELECT COUNT(*)
    FROM (
        SELECT NULL AS [EMPTY]
        ) AS [t10]
    LEFT OUTER JOIN (
        SELECT NULL AS [EMPTY]
        FROM [dbo].[PODs] AS [t11]
        WHERE [t0].[IntConNo] = [t11].[Consignment]
        ) AS [t12] ON 1=1 
    ) AS [value], [t0].[TripNumber], [t0].[DropSequence], [t0].[TripDate], [t1].[Name] AS [Depot], [t0].[Customer] AS [CustomerName], [t0].[CustomerReference], [t0].[DeliveryName], [t0].[DeliveryTown], [t0].[DeliveryPostcode], [t0].[VehicleReg] + [t0].[Subcontractor] AS [VehicleText], CONVERT(NVarChar,(
    SELECT [t16].[ID]
    FROM (
        SELECT TOP (1) [t15].[ID]
        FROM (
            SELECT NULL AS [EMPTY]
            ) AS [t13]
        LEFT OUTER JOIN (
            SELECT [t14].[ID]
            FROM [dbo].[Account] AS [t14]
            WHERE [t0].[Subcontractor] = [t14].[Name]
            ) AS [t15] ON 1=1 
        ORDER BY [t15].[ID]
        ) AS [t16]
    )) AS [SubbieID], 
    (CASE 
        WHEN [t3].[PODScanning] IS NULL THEN @p0
        ELSE [t3].[PODScanning]
     END) AS [ScanType], [t3].[ID] AS [ID3]
FROM [dbo].[Consignments] AS [t0]
INNER JOIN [dbo].[Depots] AS [t1] ON [t0].[DeliveryDepot] = [t1].[Letter]
INNER JOIN [dbo].[Account] AS [t2] ON [t0].[Customer] = [t2].[LegacyID]
INNER JOIN [dbo].[Account] AS [t3] ON [t2].[InvoiceAccount] = [t3].[LegacyID]
LEFT OUTER JOIN ((
        SELECT NULL AS [EMPTY]
        ) AS [t4]
    LEFT OUTER JOIN (
        SELECT 1 AS [test], [t5].[ID], [t5].[Consignment], [t5].[Status], [t5].[NTConsignment], [t5].[CustomerRef], [t5].[Timestamp], [t5].[SignedBy], [t5].[Clause], [t5].[BarcodeNumber], [t5].[MainRef], [t5].[Notes], [t5].[ConsignmentRef], [t5].[PODedBy]
        FROM [dbo].[PODs] AS [t5]
        ) AS [t6] ON 1=1 ) ON [t0].[IntConNo] = [t6].[Consignment]
WHERE ((NOT (EXISTS(
    SELECT TOP (1) NULL AS [EMPTY]
    FROM [dbo].[Account] AS [t7]
    WHERE [t0].[Subcontractor] = [t7].[Name]
    ORDER BY [t7].[ID]
    ))) OR (NOT (((
    SELECT [t9].[Customer]
    FROM (
        SELECT TOP (1) [t8].[Customer]
        FROM [dbo].[Account] AS [t8]
        WHERE [t0].[Subcontractor] = [t8].[Name]
        ORDER BY [t8].[ID]
        ) AS [t9]
    )) = 1))) AND ([t2].[Customer] = 1) AND ([t3].[Customer] = 1)
ORDER BY [t0].[ID], [t1].[ID], [t2].[ID], [t3].[ID], [t6].[ID]
}

var cons = (from c in dc.Consignments
            join su in dc.Accounts on c.Subcontractor equals su.Name into sug
            where (sug.FirstOrDefault() == null || sug.FirstOrDefault().Customer == false)
            join p in dc.PODs on c.IntConNo equals p.Consignment into pg
            join d in dc.Depots on c.DeliveryDepot equals d.Letter
            join sl in dc.Accounts on c.Customer equals sl.LegacyID
            join ss in dc.Accounts on sl.InvoiceAccount equals ss.LegacyID                   
            join sub in dc.Accountsubbies on ss.ID equals sub.AccountID into subg
            let firstSubContractor = sug.DefaultIfEmpty().FirstOrDefault()
            select new
            {
                           ID = c.ID,
                           IntConNo = c.IntConNo,
                           LegacyID = c.LegacyID,
                           PODs = pg.DefaultIfEmpty(),
                           TripNumber = c.TripNumber,
                           DropSequence = c.DropSequence,
                           TripDate = c.TripDate,
                           Depot = d.Name,
                           CustomerName = c.Customer,
                           CustomerReference = c.CustomerReference,
                           DeliveryName = c.DeliveryName,
                           DeliveryTown = c.DeliveryTown,
                           DeliveryPostcode = c.DeliveryPostcode,
                           VehicleText = c.VehicleReg + c.Subcontractor,
                           SubbieID = firstSubContractor == null ? "" : firstSubContractor.ID.ToString(),
                           SubbieList = subg.DefaultIfEmpty(),
                           ScanType = ss.PODScanning == null ? 0 : ss.PODScanning
              });