我对LinqToSQL很新，我正在处理的项目不能改为其他东西。我正在将一些旧的SQL代码翻译成Linq。在linq不那么热，我用Linqer为我做翻译。查询大约需要90秒才能运行，因此我认为它必须是linqToSQL。但是，当我复制LinqToSQL生成的查询并在datacontext上运行一个ExecuteQuery时，它就像我预期的那样超级快。我已经复制了完整的查询，而不是试图将其删除，但看起来问题是LinqToSQL在幕后做的事情。
总结一下，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()
它以约0.5秒的预期结果完成。 它直接在SSMS中运行大致相同的时间。但是，如果我使用创建T-SQL并执行ToList（）的linqToSQL代码，则需要很长时间。结果只有9条记录，尽管没有约束来检查余额＆lt;＆gt; 0，将有大约19,000条记录。这就好像它获得全部19,000然后检查＆lt;＆gt;获得记录后0。 我也将Linq改为将项目改为上面使用的类，而不是匿名类型，但它没有区别
这是原始的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
答案 0 :(得分：2)
我会赌钱，问题出在这一行：
where Convert.ToDecimal(g.Sum(p => p.Balance)) != 0m
可能发生的是，它无法将其转换为SQL并静默尝试从db到内存获取所有行，然后在内存对象（LINQ to objects）中进行过滤 也许尝试将其更改为：
where g.Sum(p=>.Balance!=0)
答案 1 :(得分：2)
嗯，答案结果证明不是LinqToSQL本身（虽然可能是它创建查询的方式可能受到指责），但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，我将所有变量都硬编码。当我更改它以使用Linq生成的确切sql（即使用替换的变量）时，它在SSMS中运行速度一样慢。
看看两者的执行计划，他们是完全不同的。对SO的快速搜索将我带到了这个页面：Why does a parameterized query produces vastly slower query plan vs non-parameterized query表明问题是SQL服务器的“参数嗅探”。
罪魁祸首原来是“无账号记录”字符串
为了完整性，这是Linq创建的生成的T-SQL。 将@ p10更改为实际的硬编码字符串，它将恢复全速！ 最后，我刚从linq中删除了该行，然后设置了帐户代码，一切都很好。
谢谢@ Botis，@ Blorgbeard，@ ElectricLlama＆amp; @Scott寻求建议。
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