基于行的子查询的性能调整：LEFT OUTER JOIN 和 OUTER APPLY，替代方案？

Question

某个查询（在 Dynamics CRM 2011 数据库上）的性能非常糟糕。由于它是一个规范化的数据模型，但需要对此数据（SSRS 报告）进行扁平化视图，因此我使用 SELECT TOP (1) 子查询做了很多 (12) LEFT OUTER JOIN，例如：

LEFT JOIN Filterednew_rates FRates ON FRates.new_ratesid =
    (SELECT TOP (1)
        FRR.new_ratesid
     FROM Filterednew_rates FRR
     WHERE
        FRR.new_contractid = FContract.contractid
        AND FRR.statuscode <> 803270000 -- NOT Obsolete
     ORDER BY FRR.new_startdate DESC
    )

这适用于少量结果行（例如 3 行需要 10 秒），但我已经在大约 100 个预期结果行上运行了 45 分钟（源数据量相同，只是 WHERE 不同条款）。因此，我开始寻找“强制”SQL Server 每行运行子查询的方法（从逻辑上讲，这对我来说是线性扩展的）。

然后我阅读了The power of T-SQL's APPLY operator 并设法将上面的内容更改为

OUTER APPLY (
    SELECT TOP (1)
        FRR.*
     FROM Filterednew_rates FRR
     WHERE
        FRR.new_contractid = FContract.contractid
        AND FRR.statuscode <> 803270000 -- NOT Obsolete
     ORDER BY FRR.new_startdate DESC
) AS FRates

这使得执行时间与结果记录的数量大致呈线性关系（100 行约 3:30 分钟，3 行约 6 秒）。不知何故，这使得 SQL Server 决定更好地更改查询执行计划！

在 SQL 中是否有任何其他方法可以在不借助集成/分析服务的情况下“扁平化”规范化数据模型？

编辑：

感谢@Aaron 和@BAReese 的输入。我将尝试应用 PIVOT/UNPIVOT 和窗口函数并报告查询性能差异。

根据大众的要求，查询的很大一部分。我尝试将查询“匿名化”一下，因此实际的查询属性更具描述性。

OUTER APPLY (
    SELECT TOP (1)
        FCO.*
     FROM Filterednew_contractoption FCO
     WHERE
        FCO.new_contractid = FContract.contractid
        AND FCO.new_included = 1 -- Is Included
        AND FCO.new_optionidname = 'SomeOption1'
) AS FOptionSomeOption1
OUTER APPLY (
    SELECT TOP (1)
        FCO.*
     FROM Filterednew_contractoption FCO
     WHERE
        FCO.new_contractid = FContract.contractid
        AND FCO.new_included = 1 -- Is Included
        AND FCO.new_optionidname = 'SomeOption2'
) AS FOptionSomeOption2
OUTER APPLY (
    SELECT TOP (1)
        FCD.*
     FROM FilteredContractDetail FCD
     JOIN FilteredProduct FProd ON FCD.productid = FProd.productid
     WHERE
         FContract.contractid = FCD.contractid
         AND FCD.new_included = 1 -- Is Included
         AND FProd.productnumber IN ('COLDEL1', 'COLDEL2', 'COLDEL3', 'COLDEL4')
) AS FColDelContractDetail
LEFT JOIN FilteredProduct FColDelProduct ON FColDelContractDetail.productid = FColDelProduct.productid
OUTER APPLY (
    SELECT TOP (1)
        FCO.*
     FROM Filterednew_contractoption FCO
     JOIN Filterednew_contractdetail_new_contractoptions FCD_CO ON FCO.new_contractoptionid = FCD_CO.new_contractoptionid
     WHERE
        FCD_CO.contractdetailid = FColDelContractDetail.contractdetailid
        AND FCO.new_included = 1 -- Is Included
        AND FCO.new_optionidname LIKE 'Input1'
) AS FColDelInput1Option
OUTER APPLY (
    SELECT TOP (1)
        FCO.*
     FROM Filterednew_contractoption FCO
     JOIN Filterednew_contractdetail_new_contractoptions FCD_CO ON FCO.new_contractoptionid = FCD_CO.new_contractoptionid
     WHERE
        FCD_CO.contractdetailid = FColDelContractDetail.contractdetailid
        AND FCO.new_included = 1 -- Is Included
        AND FCO.new_optionidname LIKE 'Input2'
) AS FColDelInput2Option
OUTER APPLY (
    SELECT TOP (1)
        FCO.*
     FROM Filterednew_contractoption FCO
     JOIN Filterednew_contractdetail_new_contractoptions FCD_CO ON FCO.new_contractoptionid = FCD_CO.new_contractoptionid
     WHERE
        FCD_CO.contractdetailid = FColDelContractDetail.contractdetailid
        AND FCO.new_included = 1 -- Is Included
        AND FCO.new_optionidname LIKE 'Input3'
) AS FColDelInput3Option
OUTER APPLY (
    SELECT TOP (1)
        FCP.*
     FROM Filterednew_price FCP
     WHERE FCP.new_contractid = FContract.contractid
     AND FCP.statuscode <> 803270000 -- NOT Obsolete
     ORDER BY FCP.new_validfrom DESC
) AS FPrice
OUTER APPLY (
    SELECT TOP (1)
        FCFR.*
     FROM Filterednew_contractforecastresult FCFR
     WHERE FCFR.new_contractid = FContract.contractid
     ORDER BY FCFR.createdon DESC
) AS FForecastResult

Answer 1

由于您使用的是 SQL Server，这将是使用windowing functions 提高效率的绝佳机会。

这样的事情可能会帮助它运行得更快：

LEFT JOIN
    (
    SELECT FRR.new_contractid, ROW_NUMBER() over(partition by FRR.new_contractid
                                            order by FRR.new_startdate DESC) as Last_ID
    FROM Filterednew_rates as FRR
    WHERE FRR.statuscode <> 803270000 -- NOT Obsolete
    ) AS FRates
    ON FRates.new_contractid = FContract.contractid
    and FRates.Last_ID = 1

这应该做的是允许派生表生成所有合同ID的列表，但给出优先级列表。从理论上讲，这在服务器上会更容易，并且您不会比必要的次数更多地敲桌子。您可以做的另一件事是将 SET STATISTICS IO ON 和 SET STATISTICS TIME ON 添加到查询的顶部（假设您在 SQL Server Management Studio 中对此进行测试）。如果在 SSMS 中，您将在 [Messages] 选项卡上获得一个日志，其中说明每个表的逻辑/物理读取计数是多少，以及查询所花费的时间。