在这种情况下，表变量如何提高查询性能？

8

对于这种特定情况，我将在下面尝试说明，使用表变量比不使用表变量要好。

我想知道为什么，如果可能的话，摆脱表变量。

这是使用表变量的查询：

USE [BISource_UAT]
GO

set statistics io on
SET STATISTICS TIME ON

    SET NOCOUNT ON;

    DECLARE @OrderStartDate DATETIME = '15-feb-2015'
    DECLARE @OrderEndDate DATETIME = '28-feb-2016'
    DECLARE @tmp TABLE
    (
    strBxOrderNo VARCHAR(20)
    ,sintReturnId INT
    )  

    INSERT INTO @tmp
    SELECT  strBxOrderNo
            ,sintReturnId
    FROM    TABLEBACKUPS.dbo.tblBReturnHistory rh
    WHERE   rh.sintReturnStatusId in ( 3 )
    AND     rh.dtmAdded >= @OrderStartDate
    AND     rh.dtmAdded < @OrderEndDate

    SELECT 
             op.lngPaymentID
            ,op.strBxOrderNo
            ,op.sintPaymentTypeID
            ,op.strCurrencyCode
            ,op.strBCCurrencyCode
            ,op.decPaymentAmount
            ,op.decBCPaymentAmount
            ,ap.strAccountCode
            ,o.sintMarketID
            ,o.sintOrderChannelID
            ,o.sintOrderTypeID
            ,CASE   WHEN opgv.lngpaymentID IS NULL THEN NULL
                     -- Not a Voucher = Null
                WHEN gvp.strIssuedBxOrderNo IS NULL THEN 0 ELSE 1 
              END AS [IsPromoVoucher] -- Is a Voucher - check type
            ,o.sdtmOrdCreated

    FROM    @tmp rh

            INNER JOIN TABLEBACKUPS.dbo.tblBReturn r 
                    ON r.sintReturnId = rh.sintReturnId 
                   AND r.strBxOrderNo = rh.strBxOrderNo

            INNER JOIN bocss2.dbo.tblBOrder o 
                    ON o.strBxOrderNo = r.strBxOrderNo

            INNER JOIN Bocss2.dbo.tblBOrderPayment op 
                    ON op.strBxOrderNo = o.strBxOrderNo

            INNER JOIN TABLEBACKUPS.dbo.tblBOrderItemReturn AS oir 
                    ON r.sintReturnId = oir.sintReturnID 
                   AND r.strBxOrderNo = oir.strBxOrderNo

            INNER JOIN Bocss2.dbo.tblBOrderItem AS i 
                    ON i.strBxOrderNo = oir.strBxOrderNo 
                   AND i.sintOrderSeqNo = oir.sintOrderSeqNo

            INNER JOIN TABLEBACKUPS.dbo.tblBAccountParticipant ap 
                   ON o.lngAccountParticipantID = ap.lngParticipantID

            LEFT OUTER JOIN TABLEBACKUPS.dbo.tblBOrderPaymentGiftVoucher opgv 
                         ON op.lngPaymentID = opgv.lngPaymentID

            LEFT OUTER JOIN TABLEBACKUPS.dbo.tblBGiftVoucher gv 
                         ON opgv.strVoucherNumber = gv.strVoucherNumber

            LEFT OUTER JOIN TABLEBACKUPS.dbo.tblBGiftVoucherPromotion gvp 
                         ON gvp.strIssuedBxOrderNo = gv.strIssuedBxOrderNo

    WHERE   oir.decReturnFinalAmount > 0
    AND     o.sdtmOrdCreated >= @OrderStartDate

这将产生以下统计信息：

SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.
SQL Server parse and compile time: 
   CPU time = 78 ms, elapsed time = 86 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.
Table '#BF0B2154'. Scan count 0, logical reads 1957, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBReturnHistory'. Scan count 1, logical reads 13, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

 SQL Server Execution Times:
   CPU time = 16 ms,  elapsed time = 9 ms.
Table 'tblBGiftVoucherPromotion'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBGiftVoucher'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderPaymentGiftVoucher'. Scan count 0, logical reads 452, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderItem'. Scan count 0, logical reads 904, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderPayment'. Scan count 186, logical reads 1649, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBAccountParticipant'. Scan count 0, logical reads 7112, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrder'. Scan count 3557, logical reads 14267, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderItemReturn'. Scan count 1951, logical reads 5865, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBReturn'. Scan count 0, logical reads 3902, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table '#BF0B2154'. Scan count 1, logical reads 7, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

 SQL Server Execution Times:
   CPU time = 125 ms,  elapsed time = 138 ms.
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

在 我想显示查询计划上使用showplan_text：

查询的第一部分-填充表变量 在此处输入图片说明

查询的第二部分：使用表变量并联接其他表： 在此处输入图片说明

这是使用表变量进行查询的XML计划。

现在，这是同一查询，但未使用表变量：

USE [BISource_UAT]
GO

set statistics io on
SET STATISTICS TIME ON

    SET NOCOUNT ON;

    DECLARE @OrderStartDate DATETIME = '15-feb-2015'
    DECLARE @OrderEndDate DATETIME = '28-feb-2016'

    SELECT 
             op.lngPaymentID
            ,op.strBxOrderNo
            ,op.sintPaymentTypeID
            ,op.strCurrencyCode
            ,op.strBCCurrencyCode
            ,op.decPaymentAmount
            ,op.decBCPaymentAmount
            ,ap.strAccountCode
            ,o.sintMarketID
            ,o.sintOrderChannelID
            ,o.sintOrderTypeID
            ,CASE   WHEN opgv.lngpaymentID IS NULL 
               THEN NULL -- Not a Voucher = Null
                WHEN gvp.strIssuedBxOrderNo IS NULL 
                THEN 0 ELSE 1 END AS [IsPromoVoucher] 
                -- Is a Voucher - check type
            ,o.sdtmOrdCreated

    FROM    TABLEBACKUPS.dbo.tblBReturnHistory rh

            INNER JOIN TABLEBACKUPS.dbo.tblBReturn r 
                    ON r.sintReturnId = rh.sintReturnId 
                   AND r.strBxOrderNo = rh.strBxOrderNo

            INNER JOIN bocss2.dbo.tblBOrder o 
                    ON o.strBxOrderNo = r.strBxOrderNo
                   AND o.sdtmOrdCreated >= @OrderStartDate

            INNER JOIN Bocss2.dbo.tblBOrderPayment op 
                    ON op.strBxOrderNo = o.strBxOrderNo

            INNER JOIN TABLEBACKUPS.dbo.tblBOrderItemReturn AS oir 
                    ON r.sintReturnId = oir.sintReturnID 
                   AND r.strBxOrderNo = oir.strBxOrderNo
                   AND oir.decReturnFinalAmount > 0

            INNER JOIN Bocss2.dbo.tblBOrderItem AS i 
                    ON i.strBxOrderNo = oir.strBxOrderNo 
                   AND i.sintOrderSeqNo = oir.sintOrderSeqNo

            INNER JOIN TABLEBACKUPS.dbo.tblBAccountParticipant ap 
                   ON o.lngAccountParticipantID = ap.lngParticipantID

            LEFT OUTER JOIN TABLEBACKUPS.dbo.tblBOrderPaymentGiftVoucher opgv 
                         ON op.lngPaymentID = opgv.lngPaymentID

            LEFT OUTER JOIN TABLEBACKUPS.dbo.tblBGiftVoucher gv 
                         ON opgv.strVoucherNumber = gv.strVoucherNumber

            LEFT OUTER JOIN TABLEBACKUPS.dbo.tblBGiftVoucherPromotion gvp 
                         ON gvp.strIssuedBxOrderNo = gv.strIssuedBxOrderNo

    WHERE   rh.sintReturnStatusId in ( 3 )
    AND     rh.dtmAdded >= @OrderStartDate
    AND     rh.dtmAdded < @OrderEndDate

在查看统计信息时，这就是我们得到的：

SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBGiftVoucher'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBAccountParticipant'. Scan count 1, logical reads 32, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBReturn'. Scan count 1, logical reads 170, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderItemReturn'. Scan count 0, logical reads 35849, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderPayment'. Scan count 9408, logical reads 87643, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderItem'. Scan count 1950, logical reads 8336, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrder'. Scan count 1951, logical reads 7835, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBReturnHistory'. Scan count 1, logical reads 13, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBOrderPaymentGiftVoucher'. Scan count 1, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'tblBGiftVoucherPromotion'. Scan count 1, logical reads 27, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

 SQL Server Execution Times:
   CPU time = 625 ms,  elapsed time = 612 ms.
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 0 ms.

 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 0 ms.

现在，关于文本格式的执行计划：

设定参数

在此处输入图片说明

现在，重要的是运行节目： 在此处输入图片说明

这是不使用表变量的查询的XML计划。

但是，为什么使用表变量读取次数减少，I / O减少以及执行（不清除缓存）的速度总是更快？

我可以提供任何创建表脚本或任何其他必要的信息，以更好地了解这种情况。

只需在此处发表任何评论，我就会回复。

这是一个类似的问题：

在这种情况下，为什么使用表变量的速度是#temp表的两倍？

在CHECKPOINT之后运行查询时；DBCC DROPCLEANBUFFERS ; 结果是：

用表变量查询

用表变量查询

没有表变量的查询

没有表变量的查询

sql-server  sql-server-2014  query-performance  temporary-tables  table-variable 
— 马切洛·米奥雷利（Marcello Miorelli）
source
如果将第一个查询的where条件过滤器保留在第二个查询的where条件中，而不是将它们移至内部联接条件，会有什么区别？这：WHERE oir.decReturnFinalAmount> 0 AND o.sdtmOrdCreated> = @OrderStartDate
— BateTech
当我将条件从INNER JOINS内部移动到WHERE子句时，@ BateTech在清除缓存后，CPU时间从203增大到281，经过时间从865增大到4029。某些表的逻辑读取也增加了。
— Marcello Miorelli '16

Answers:

8

发挥作用的主要因素是：

  • 优化器不会尝试找到最佳计划；它的目标是快速找到合理的计划
  • 假设查询将在冷缓存中运行
  • 与随机I / O相比，使用的成本模型更倾向于顺序I / O
  • 假设重复搜索索引是随机分布的

表变量的基数估计为1行（除非发生语句级重新编译，否则跟踪标志2453处于活动状态）。如此低的估算结果导致了一项非常低成本的计划，该计划具有基于嵌套循环的导航策略。对于相对较少的行数，此计划可能会继续有效，尤其是在不需要从持久性存储中读取所需数据的情况下。

通过更准确的基数估计，优化器倾向于使用哈希联接和几次扫描的计划。考虑到上面列出的假设，这似乎比导航策略便宜。特别是关于冷高速缓存，以及与许多搜索（假定很大程度上是随机I / O模式）相比，顺序扫描的成本相对较低。

如果所需数据不在内存中，则表变量计划可能会比替代方案慢，或者可能不在。成本模型正是这样一个模型-使用的确切数字可能无法代表您的硬件和配置，并且所作的假设在特定情况下可能无效。

所有这些警告特别适用于低成本查询（两者都是），因为小的成本变化会产生非常不同的计划形状。实际上，两个计划都是成功的，因为它们足够快速，有效地产生了结果。

— 保罗·怀特9
source
By using our site, you acknowledge that you have read and understand our Cookie Policy and Privacy Policy.
Licensed under cc by-sa 3.0 with attribution required.