Question

我有一个视图，其中有一个未编入索引的列在另一个查询中连接。我们无法在视图中创建索引，因为它使用外连接。

外部查询基本上是：

select * from SomeTable AS T INNER JOIN
v_SomeView AS V ON T.Column = V.Column

查询非常缓慢，通过一些实验，我们发现将查询更改为：

select * from SomeTable AS T INNER JOIN
(select TOP 10000000 * from v_SomeView) AS V ON T.Column = V.Column

加快了查询速度（10分钟到5秒左右）。

视图中只有大约1000行。

有人可以解释这里发生的事情会对性能产生如此巨大的影响吗？

执行计划：

http://dropcanvas.com/011il

以下是实际视图 v_SecurityClassificationResult ：

SELECT        rc.SecurityId, rc.Status, rc.ExpiryDate, rc.StartDate, rc.ClassificationValue AS RiskClass, sg.ClassificationValue AS SecurityGroup, 
                         br.ClassificationValue AS BondRating, cur.ClassificationValue AS Currency, cod.ClassificationValue AS Country, reg.ClassificationValue AS Region
FROM            dbo.SecurityClassificationResult AS rc LEFT OUTER JOIN
                         dbo.SecurityClassificationResult AS sg ON rc.SecurityId = sg.SecurityId AND rc.ExpiryDate = sg.ExpiryDate AND sg.SecurityClassificationFieldId =
                             (SELECT        SecurityClassificationFieldId
                               FROM            dbo.SecurityClassificationField
                               WHERE        (ClassificationField = 'SecurityGroup')) LEFT OUTER JOIN
                         dbo.SecurityClassificationResult AS br ON rc.SecurityId = br.SecurityId AND sg.ExpiryDate = br.ExpiryDate AND br.SecurityClassificationFieldId =
                             (SELECT        SecurityClassificationFieldId
                               FROM            dbo.SecurityClassificationField
                               WHERE        (ClassificationField = 'BondRating')) LEFT OUTER JOIN
                         dbo.SecurityClassificationResult AS cur ON rc.SecurityId = cur.SecurityId AND br.ExpiryDate = cur.ExpiryDate AND cur.SecurityClassificationFieldId =
                             (SELECT        SecurityClassificationFieldId
                               FROM            dbo.SecurityClassificationField
                               WHERE        (ClassificationField = 'Currency')) LEFT OUTER JOIN
                         dbo.SecurityClassificationResult AS cod ON rc.SecurityId = cod.SecurityId AND cur.ExpiryDate = cod.ExpiryDate AND cod.SecurityClassificationFieldId =
                             (SELECT        SecurityClassificationFieldId
                               FROM            dbo.SecurityClassificationField
                               WHERE        (ClassificationField = 'CountryOfDomicile')) LEFT OUTER JOIN
                         dbo.SecurityClassificationResult AS reg ON rc.SecurityId = reg.SecurityId AND cod.ExpiryDate = reg.ExpiryDate AND reg.SecurityClassificationFieldId =
                             (SELECT        SecurityClassificationFieldId
                               FROM            dbo.SecurityClassificationField
                               WHERE        (ClassificationField = 'Region'))
WHERE        (rc.SecurityClassificationFieldId =
                             (SELECT        SecurityClassificationFieldId
                               FROM            dbo.SecurityClassificationField
                               WHERE        (ClassificationField = 'RiskClass')))

以及从中选择的另一个查询：

SELECT        count(*)
FROM            dbo.Fund_RelevantSecurity AS FRS INNER JOIN
                         dbo.SourceSystemImportLog AS SSIL ON FRS.SourceSystemImporLogtId = SSIL.SourceSystemImporLogtId INNER JOIN
                         dbo.FundInstanceHolding AS FIH ON FRS.FundInstanceHoldingId = FIH.FundInstanceHoldingId INNER JOIN
                         dbo.FundInstance AS FI ON FIH.FundInstanceId = FI.FundInstanceId INNER JOIN
                         dbo.SourceSystemImportLog AS SSILOrig ON SSILOrig.SourceSystemImporLogtId = FI.SourceSystemImportLogId INNER JOIN
                         dbo.Security ON FRS.SecurityId = dbo.Security.SecurityId INNER JOIN
                         dbo.Fund ON FRS.FundId = dbo.Fund.FundId INNER JOIN
                         dbo.BusinessUnitFund ON dbo.Fund.FundId = dbo.BusinessUnitFund.FundId INNER JOIN
                         dbo.BusinessUnit ON dbo.BusinessUnit.BusinessUnitId = dbo.BusinessUnitFund.BusinessUnitId RIGHT OUTER JOIN
                         (select top 2147483647 * from dbo.v_SecurityClassificationResult) AS classificationResult ON FRS.SecurityId = classificationResult.SecurityId AND GETDATE() 
                         <= classificationResult.ExpiryDate AND GETDATE() >= classificationResult.StartDate
WHERE        (SSIL.ImportStatusId <> 5)

Answer 1

我建议您重建索引并刷新统计信息。通过做TOP N你的优化器采取另一个计划，似乎这个更好。尝试检查预期和实际的记录数量，以找出计划错误的位置。另一件事是，如果重写视图，可能会获得更好的性能。您可以执行类似的操作（无法检查语法和逻辑，因为没有提供结构和数据）：

SELECT
    rc.SecurityId ,
    rc.Status ,
    rc.ExpiryDate ,
    rc.StartDate ,
    s.ClassificationValue AS RiskClass ,
    MIN(CASE WHEN s.ClassificationValue = 'SecurityGroup' THEN s.ClassificationValue END) AS SecurityGroup ,
    MIN(CASE WHEN s.ClassificationValue = 'BondRating' THEN s.ClassificationValue END) AS BondRating ,
    MIN(CASE WHEN s.ClassificationValue = 'Currency' THEN s.ClassificationValue END) AS Currency ,
    MIN(CASE WHEN s.ClassificationValue = 'CountryOfDomicile' THEN s.ClassificationValue END) AS Country ,
    MIN(CASE WHEN s.ClassificationValue = 'Region' THEN s.ClassificationValue END) AS Region
FROM
    dbo.SecurityClassificationResult AS rc
    LEFT OUTER JOIN
    (
    SELECT s.ClassificationValue,
            sf.ClassificationField
    FROM  dbo.SecurityClassificationResult AS s
    JOIN dbo.SecurityClassificationField AS sf
      ON sf.SecurityClassificationFieldId = s.SecurityClassificationFieldId
    WHERE sf.ClassificationField IN ( 'SecurityGroup', 'BondRating', 'Currency', 'CountryOfDomicile' 'Region')

    ) s
    ON s.SecurityId = rc.SecurityId
WHERE
    ( rc.SecurityClassificationFieldId = (
                                           SELECT
                                            SecurityClassificationFieldId
                                           FROM
                                            dbo.SecurityClassificationField
                                           WHERE
                                            ( ClassificationField = 'RiskClass' )
                                         ) )
GROUP BY     rc.SecurityId ,
    rc.Status ,
    rc.ExpiryDate ,
    rc.StartDate ,
    s.ClassificationValue

为什么加入选择前N个视图比加入视图要快得多？

1 个答案: