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我对 LinqToSQL 很陌生，我正在从事的项目不能更改为其他项目。我正在将一些旧的 SQL 代码翻译成 Linq。对 linq 没有那么热情，我使用 Linqer 为我做翻译。查询运行大约需要 90 秒，所以我认为它一定是 linqToSQL。但是，当我复制 LinqToSQL 生成的查询并在数据上下文上运行 ExecuteQuery 时，它的速度和我预期的一样快。我已经复制了完整的查询，而不是试图将其提取出来，但看起来问题出在 LinqToSQL 在幕后所做的事情上。

总而言之，如果我复制 linq 创建的 T-SQL 并运行

var results = DB.ExecuteQuery<InvoiceBalanceCheckDTO.InvoiceBalanceCheck>(@"T-SQL created by Linq - see below").ToList()

它在大约 0.5 秒内完成预期结果。它直接在 SSMS 中几乎同时运行。但是，如果我使用创建 T-SQL 的 linqToSQL 代码并执行 ToList() 则需要很长时间。结果只有 9 条记录，尽管没有检查余额 <> 0 的约束，大约有 19,000 条记录。就好像它得到了所有 19,000，然后在获得记录后检查 <> 0。我还将 Linq 更改为投影到上面使用的类中，而不是匿名类型，但这没什么区别

这是原始 SQL：

SELECT InvoiceNum, Max(AccountCode), Sum(AmountInc) AS Balance
FROM 
    (SELECT InvoiceNum, AccountCode, AmountInc From TourBookAccount WHERE AccDetailTypeE IN(20,30) AND InvoiceNum >= 1000 
    UNION ALL 
    SELECT InvoiceNum, '<no matching invoice>' AS AccountCode, AccountInvoiceDetail.AmountInc 
    FROM AccountInvoiceDetail 
        INNER JOIN AccountInvoice ON AccountInvoiceDetail.InvoiceID=AccountInvoice.InvoiceID 
    WHERE AccDetailTypeE IN(20,30) 
    AND InvoiceNum >= 1000 
    ) as t
GROUP BY InvoiceNum 
HAVING (Sum(t.AmountInc)<>0) 
ORDER BY InvoiceNum

这是 linq

var test =  (from t in
                        (
                            //this gets the TourBookAccount totals
                            from tba in DB.TourBookAccount
                            where
                            detailTypes.Contains(tba.AccDetailTypeE) &&
                            tba.InvoiceNum >= dto.CheckInvoiceNumFrom
                            select new 
                            {
                                InvoiceNum = tba.InvoiceNum,
                                AccountCode = tba.AccountCode,
                                Balance = tba.AmountInc
                            }
                        )
                        .Concat //note that concat, since it's possible that the AccountInvoice record does not actually exist
                        (
                            //this gets the Invoice detail totals.
                            from aid in DB.AccountInvoiceDetail
                            where
                            detailTypes.Contains(aid.AccDetailTypeE) &&
                            aid.AccountInvoice.InvoiceNum >= dto.CheckInvoiceNumFrom &&
                            select new 
                            {
                                InvoiceNum = aid.AccountInvoice.InvoiceNum,
                                AccountCode = "<No Account Records>",
                                Balance = aid.AmountInc
                            }
                        ) 
                group t by t.InvoiceNum into g
                where Convert.ToDecimal(g.Sum(p => p.Balance)) != 0m
                select new 
                {
                    InvoiceNum = g.Key,
                    AccountCode = g.Max(p => p.AccountCode),
                    Balance = g.Sum(p => p.Balance)
                }).ToList();

这是 linq 生成的 T-SQL

  SELECT [t5].[InvoiceNum], [t5].[value2] AS [AccountCode], [t5].[value3] AS [Balance]
FROM (
    SELECT SUM([t4].[AmountInc]) AS [value], MAX([t4].[AccountCode]) AS [value2], SUM([t4].[AmountInc]) AS [value3], [t4].[InvoiceNum]
    FROM (
        SELECT [t3].[InvoiceNum], [t3].[AccountCode], [t3].[AmountInc]
        FROM (
            SELECT [t0].[InvoiceNum], [t0].[AccountCode], [t0].[AmountInc]
            FROM [dbo].[TourBookAccount] AS [t0]
            WHERE ([t0].[AccDetailTypeE] IN (20, 30)) AND ([t0].[InvoiceNum] >= 1000)
            UNION ALL
            SELECT [t2].[InvoiceNum],'<No Account Records>' AS [value], [t1].[AmountInc]
            FROM [dbo].[AccountInvoiceDetail] AS [t1]
            INNER JOIN [dbo].[AccountInvoice] AS [t2] ON [t2].[InvoiceID] = [t1].[InvoiceID]
            WHERE ([t1].[AccDetailTypeE] IN (20, 30)) AND ([t2].[InvoiceNum] >= 1000)
            ) AS [t3]
        ) AS [t4]
    GROUP BY [t4].[InvoiceNum]
    ) AS [t5]
WHERE [t5].[value] <> 0
4

2 回答 2

2

我敢打赌，问题出在这一行：

where Convert.ToDecimal(g.Sum(p => p.Balance)) != 0m

可能发生的事情是，它无法将其转换为 SQL 并默默地尝试将所有行从 db 获取到内存，然后在内存对象（LINQ to objects）上进行过滤也许尝试将其更改为类似：

where g.Sum(p=>.Balance!=0)
于 2013-08-26T04:47:24.997 回答
2

好吧，结果证明不是 LinqToSQL 本身（尽管可能要归咎于它创建查询的方式），而是 SQL 服务器处理查询的方式。当我在数据库上运行查询以检查速度（并在 DB.ExecuteQuery 中运行创建的 T=SQL）时，我对所有变量进行了硬编码。当我将其更改为使用 Linq 生成的确切 sql（即使用被替换的变量）时，它在 SSMS 中的运行速度同样慢。

看两人的执行计划，大相径庭。对 SO 的快速搜索将我带到了这个页面：为什么参数化查询产生的查询计划与非参数化查询相比要慢得多，这表明问题是 SQL 服务器的“参数嗅探”。

罪魁祸首原来是“无帐户记录”字符串

为了完整起见，这里是 Linq 创建的生成的 T-SQL。将@p10 更改为实际的硬编码字符串，它会恢复全速！最后，我只是从 linq 中删除了该行，然后设置了帐户代码，一切都很好。

感谢@Botis、@Blorgbeard、@ElectricLlama 和@Scott 的建议。

DECLARE @p0 as Int = 20
DECLARE @p1 as Int = 30
DECLARE @p2 as Int = 1000
DECLARE @p3 as Int = 20
DECLARE @p4 as Int = 30
DECLARE @p5 as Int = 1000
DECLARE @p6 as Int = 40
DECLARE @p7 as Int = 10
DECLARE @p8 as Int = 0
DECLARE @p9 as Int = 1
DECLARE @p10 as NVarChar(4000)= '<No Account Records>' /*replace this parameter with the actual text in the SQl and it's way faster.*/
DECLARE @p11 as Decimal(33,4) = 0


SELECT [t5].[InvoiceNum], [t5].[value2] AS [AccountCode], [t5].[value3] AS [Balance]
FROM (
    SELECT SUM([t4].[AmountInc]) AS [value], MAX([t4].[AccountCode]) AS [value2], SUM([t4].[AmountInc]) AS [value3], [t4].[InvoiceNum]
    FROM (
        SELECT [t3].[InvoiceNum], [t3].[AccountCode], [t3].[AmountInc]
        FROM (
            SELECT [t0].[InvoiceNum], [t0].[AccountCode], [t0].[AmountInc]
            FROM [dbo].[TourBookAccount] AS [t0]
            WHERE ([t0].[AccDetailTypeE] IN (@p0, @p1)) AND ([t0].[InvoiceNum] >= @p2)
            UNION ALL
            SELECT [t2].[InvoiceNum], @p10 AS [value], [t1].[AmountInc]
            FROM [dbo].[AccountInvoiceDetail] AS [t1]
            INNER JOIN [dbo].[AccountInvoice] AS [t2] ON [t2].[InvoiceID] = [t1].[InvoiceID]
            WHERE ([t1].[AccDetailTypeE] IN (@p3, @p4)) AND ([t2].[InvoiceNum] >= @p5) AND ([t2].[InvoiceStatusE] <= @p6) AND ([t2].[InvoiceTypeE] = @p7) AND ([t1].[BookNum] <> @p8) AND ([t1].[AccDetailSourceE] = @p9)
            ) AS [t3]
        ) AS [t4]
    GROUP BY [t4].[InvoiceNum]
    ) AS [t5]
WHERE [t5].[value] <> @p11


SELECT [t5].[InvoiceNum], [t5].[value2] AS [AccountCode], [t5].[value3] AS [Balance]
FROM (
    SELECT SUM([t4].[AmountInc]) AS [value], MAX([t4].[AccountCode]) AS [value2], SUM([t4].[AmountInc]) AS [value3], [t4].[InvoiceNum]
    FROM (
        SELECT [t3].[InvoiceNum], [t3].[AccountCode], [t3].[AmountInc]
        FROM (
            SELECT [t0].[InvoiceNum], [t0].[AccountCode], [t0].[AmountInc]
            FROM [dbo].[TourBookAccount] AS [t0]
            WHERE ([t0].[AccDetailTypeE] IN (20, 30)) AND ([t0].[InvoiceNum] >= 1000)
            UNION ALL
            SELECT [t2].[InvoiceNum], '<No Account Records>' AS [value], [t1].[AmountInc]
            FROM [dbo].[AccountInvoiceDetail] AS [t1]
            INNER JOIN [dbo].[AccountInvoice] AS [t2] ON [t2].[InvoiceID] = [t1].[InvoiceID]
            WHERE ([t1].[AccDetailTypeE] IN (20, 30)) AND ([t2].[InvoiceNum] >= 0) AND ([t2].[InvoiceStatusE] <= 40) AND ([t2].[InvoiceTypeE] = 10) AND ([t1].[BookNum] <> 0) AND ([t1].[AccDetailSourceE] = 1)
            ) AS [t3]
        ) AS [t4]
    GROUP BY [t4].[InvoiceNum]
    ) AS [t5]
WHERE [t5].[value] <> 0
于 2013-08-29T00:35:05.437 回答