我试图在LinQ中编写一个简单的SQL查询，无论我怎么努力，我总是得到一个复杂的查询。
这是我想要实现的SQL（这不是我得到的）：
SELECT
ClearingAccounts.ID,
SUM(CASE WHEN Payments.StatusID = 1 THEN Payments.TotalAmount ELSE 0 END) AS Sum1,
SUM(CASE WHEN DirectDebits.StatusID = 2 THEN DirectDebits.TotalAmount ELSE 0 END) AS Sum2,
SUM(CASE WHEN Payments.StatusID = 2 THEN Payments.TotalAmount ELSE 0 END) AS Sum3,
SUM(CASE WHEN DirectDebits.StatusID = 1 THEN DirectDebits.TotalAmount ELSE 0 END) AS Sum4
FROM ClearingAccounts
LEFT JOIN Payments ON Payments.ClearingAccountID = ClearingAccounts.ID
LEFT JOIN DirectDebits ON DirectDebits.ClearingAccountID = ClearingAccounts.ID
GROUP BY ClearingAccounts.ID
以下是代码：
from clearingAccount in clearingAccounts
let payments = clearingAccount.Payments
let directDebits = clearingAccount.DirectDebits
select new
{
ID = clearingAccount.ID,
Sum1 = payments.Sum(p => p.StatusID == 1 ? p.TotalAmount : 0),
Sum2 = directDebits.Sum(p => p.StatusID == 2 ? p.TotalAmount : 0),
Sum3 = payments.Sum(p => p.StatusID == 2 ? p.TotalAmount : 0),
Sum4 = directDebits.Sum(p => p.StatusID == 1 ? p.TotalAmount : 0),
}
生成的查询从每个总和的相应表中获取数据，因此四次。我不确定是否可以优化它？
编辑这里是生成的查询：
SELECT
[Project5].[ID] AS [ID],
[Project5].[C1] AS [C1],
[Project5].[C2] AS [C2],
[Project5].[C3] AS [C3],
[Project5].[C4] AS [C4]
FROM ( SELECT
[Project4].[ID] AS [ID],
[Project4].[C1] AS [C1],
[Project4].[C2] AS [C2],
[Project4].[C3] AS [C3],
(SELECT
SUM([Filter5].[A1]) AS [A1]
FROM ( SELECT
CASE WHEN (1 = [Extent5].[StatusID]) THEN [Extent5].[TotalAmount] ELSE cast(0 as decimal(18)) END AS [A1]
FROM [dbo].[DirectDebits] AS [Extent5]
WHERE [Project4].[ID] = [Extent5].[ClearingAccountID]
) AS [Filter5]) AS [C4]
FROM ( SELECT
[Project3].[ID] AS [ID],
[Project3].[C1] AS [C1],
[Project3].[C2] AS [C2],
(SELECT
SUM([Filter4].[A1]) AS [A1]
FROM ( SELECT
CASE WHEN (2 = [Extent4].[StatusID]) THEN [Extent4].[TotalAmount] ELSE cast(0 as decimal(18)) END AS [A1]
FROM [dbo].[Payments] AS [Extent4]
WHERE [Project3].[ID] = [Extent4].[ClearingAccountID]
) AS [Filter4]) AS [C3]
FROM ( SELECT
[Project2].[ID] AS [ID],
[Project2].[C1] AS [C1],
(SELECT
SUM([Filter3].[A1]) AS [A1]
FROM ( SELECT
CASE WHEN (2 = [Extent3].[StatusID]) THEN [Extent3].[TotalAmount] ELSE cast(0 as decimal(18)) END AS [A1]
FROM [dbo].[DirectDebits] AS [Extent3]
WHERE [Project2].[ID] = [Extent3].[ClearingAccountID]
) AS [Filter3]) AS [C2]
FROM ( SELECT
[Project1].[ID] AS [ID],
(SELECT
SUM([Filter2].[A1]) AS [A1]
FROM ( SELECT
CASE WHEN (1 = [Extent2].[StatusID]) THEN [Extent2].[TotalAmount] ELSE cast(0 as decimal(18)) END AS [A1]
FROM [dbo].[Payments] AS [Extent2]
WHERE [Project1].[ID] = [Extent2].[ClearingAccountID]
) AS [Filter2]) AS [C1]
FROM ( SELECT
[Extent1].[ID] AS [ID]
FROM [dbo].[ClearingAccounts] AS [Extent1]
WHERE ([Extent1].[CustomerID] = 3) AND ([Extent1].[Deleted] <> 1)
) AS [Project1]
) AS [Project2]
) AS [Project3]
) AS [Project4]
) AS [Project5]
答案 0 :(得分：1)
修改
请注意，根据@ usr的评论，您的原始Sql查询已损坏。通过LEFT OUTER连接两个独立的表，然后对公共连接键进行分组，只要其中一个DirectDebits或Payments表返回多行，就会错误地复制其他＆＃39;中的TotalAmount值SUMmed colums（反之亦然）。例如如果给定的ClearingAccount有3个DirectDebits和4个Payments，您将获得总共12行（而您应该为这两个表独立地汇总3行和4行）。更好的Sql Query将是：
WITH ctePayments AS
(
SELECT
ClearingAccounts.ID,
-- Note the ELSE 0 projection isn't required as nulls are eliminated from aggregates
SUM(CASE WHEN Payments.StatusID = 1 THEN Payments.TotalAmount END) AS Sum1,
SUM(CASE WHEN Payments.StatusID = 2 THEN Payments.TotalAmount END) AS Sum3
FROM ClearingAccounts
INNER JOIN Payments ON Payments.ClearingAccountID = ClearingAccounts.ID
GROUP BY ClearingAccounts.ID
),
cteDirectDebits AS
(
SELECT
ClearingAccounts.ID,
SUM(CASE WHEN DirectDebits.StatusID = 2 THEN DirectDebits.TotalAmount END) AS Sum2,
SUM(CASE WHEN DirectDebits.StatusID = 1 THEN DirectDebits.TotalAmount END) AS Sum4
FROM ClearingAccounts
INNER JOIN DirectDebits ON DirectDebits.ClearingAccountID = ClearingAccounts.ID
GROUP BY ClearingAccounts.ID
)
SELECT ca.ID, COALESCE(p.Sum1, 0) AS Sum1, COALESCE(d.Sum2, 0) AS Sum2,
COALESCE(p.Sum3, 0) AS Sum3, COALESCE(d.Sum4, 0) AS Sum4
FROM
ClearingAccounts ca
LEFT OUTER JOIN ctePayments p
ON ca.ID = p.ID
LEFT OUTER JOIN cteDirectDebits d
ON ca.ID = d.ID;
-- GROUP BY not required, since we have already guaranteed at most one row
-- per joined table in the CTE's, assuming ClearingAccounts.ID is unique;
在您考虑转换为LINQ之前，您想要使用测试用例进行修复和测试。
旧答案
Sql构造：
SELECT SUM(CASE WHEN ... THEN 1 ELSE 0 END) AS Something
在SELECT列表中应用时，是一种常见的 hack ＆＃39;替代＆＃39;从更大的数据转移数据选择符合投影标准的列（如果不匹配则选择零）。它根本不是一个总和，它是一个匹配的＆＃39;计数。
关于优化生成的Sql，另一种方法是在加入和分组后实现数据（当然，如果有谓词{{1}}子句，也可以通过IQueryable在Sql中应用它），以及然后在内存中进行条件求和：
WHERE但是，就个人而言，我会将此数据投影直接保留在Sql中，然后使用类似SqlQuery的内容然后从Sql反序列化结果 直接进入最终的实体类型。
答案 1 :(得分：-1)
1） 在EF中添加AsNoTracking以避免跟踪更改。
检查您对JOIN使用的列是否有索引。特别是您用于分组的列。描述查询并对其进行优化。 EF还存储过程的开销。
或
2）如果找不到按照需要快速生成的方法，创建存储过程并从EF 调用它。即使是相同的查询也会更快。