为什么我会得到从 Int / Smallint 到 Varchar 的隐式转换，它真的会影响基数估计吗？

Question

为什么我会得到从 Int / Smallint 到 Varchar 的隐式转换，它真的会影响基数估计吗？

Voy*_*ead 11 sql-server execution-plan type-conversion cardinality-estimates sql-server-2017

我正在尝试对实际执行计划使用显示计划分析 (SSMS) 来解决执行缓慢的查询。分析工具指出，在计划中的几个地方，对行数的估计与返回的结果不一致，并进一步给了我一些隐式转换警告。

我不明白这些 int 到 Varchar 的隐式转换 - 引用的字段不是查询中任何参数/过滤器的一部分，并且在所有涉及的表中，列数据类型是相同的：

我收到以下 CardinalityEstimate 警告：

表达式中的类型转换 (CONVERT_IMPLICIT(varchar(12),[ccd].[profileid],0)) 可能会影响查询计划选择中的“CardinalityEstimate”——这个字段在我的数据库中到处都是整数

表达式中的类型转换 (CONVERT_IMPLICIT(varchar(6),[ccd].[nodeid],0)) 可能会影响查询计划选择中的“CardinalityEstimate”——这个字段在我的数据库中到处都是 smallint

表达式中的类型转换 (CONVERT_IMPLICIT(varchar(6),[ccd].[sessionseqnum],0)) 可能会影响查询计划选择中的“CardinalityEstimate”——这个字段在我的数据库中到处都是 smallint

表达式中的类型转换 (CONVERT_IMPLICIT(varchar(41),[ccd].[sessionid],0)) 可能会影响查询计划选择中的“CardinalityEstimate”——这个字段在我的数据库中到处都是小数

[编辑]这里是查询和实际执行计划供参考 https://www.brentozar.com/pastetheplan/?id=SysYt0NzN

和表定义..

/****** Object:  Table [dbo].[agentconnectiondetail]    Script Date: 1/10/2019 9:10:04 AM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[agentconnectiondetail](
    [sessionid] [decimal](18, 0) NOT NULL,
    [sessionseqnum] [smallint] NOT NULL,
    [nodeid] [smallint] NOT NULL,
    [profileid] [int] NOT NULL,
    [resourceid] [int] NOT NULL,
    [startdatetime] [datetime2](7) NOT NULL,
    [enddatetime] [datetime2](7) NOT NULL,
    [qindex] [smallint] NOT NULL,
    [gmtoffset] [smallint] NOT NULL,
    [ringtime] [smallint] NULL,
    [talktime] [smallint] NULL,
    [holdtime] [smallint] NULL,
    [worktime] [smallint] NULL,
    [callwrapupdata] [varchar](40) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,
    [callresult] [smallint] NULL,
    [dialinglistid] [int] NULL,
    [convertedStartDatetimelocal] [datetime2](7) NULL,
    [convertedEndDatetimelocal] [datetime2](7) NULL,
 CONSTRAINT [PK_agentconnectiondetail] PRIMARY KEY CLUSTERED 
(
    [sessionid] ASC,
    [sessionseqnum] ASC,
    [nodeid] ASC,
    [profileid] ASC,
    [resourceid] ASC,
    [startdatetime] ASC,
    [qindex] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
/****** Object:  Table [dbo].[contactcalldetail]    Script Date: 1/10/2019 9:10:04 AM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[contactcalldetail](
    [sessionid] [decimal](18, 0) NOT NULL,
    [sessionseqnum] [smallint] NOT NULL,
    [nodeid] [smallint] NOT NULL,
    [profileid] [int] NOT NULL,
    [contacttype] [smallint] NOT NULL,
    [contactTypeDescription] [varchar](20) COLLATE Latin1_General_CI_AS NULL,
    [contactdisposition] [smallint] NOT NULL,
    [contactdispositionDescription] [varchar](20) COLLATE Latin1_General_CI_AS NULL,
    [dispositionreason] [varchar](100) COLLATE Latin1_General_CI_AS NULL,
    [originatortype] [smallint] NOT NULL,
    [originatorTypeDescription] [varchar](20) COLLATE Latin1_General_CI_AS NULL,
    [originatorid] [int] NULL,
    [originatordn] [varchar](30) COLLATE Latin1_General_CI_AS NULL,
    [destinationtype] [smallint] NULL,
    [destinationTypeDescription] [varchar](20) COLLATE Latin1_General_CI_AS NULL,
    [destinationid] [int] NULL,
    [destinationdn] [varchar](30) COLLATE Latin1_General_CI_AS NULL,
    [startdatetimeUTC] [datetime2](7) NOT NULL,
    [enddatetimeUTC] [datetime2](7) NOT NULL,
    [gmtoffset] [smallint] NOT NULL,
    [callednumber] [varchar](30) COLLATE Latin1_General_CI_AS NULL,
    [origcallednumber] [varchar](30) COLLATE Latin1_General_CI_AS NULL,
    [applicationtaskid] [decimal](18, 0) NULL,
    [applicationid] [int] NULL,
    [applicationname] [varchar](30) COLLATE Latin1_General_CI_AS NULL,
    [connecttime] [smallint] NULL,
    [customvariable1] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable2] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable3] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable4] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable5] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable6] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable7] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable8] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable9] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [customvariable10] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [accountnumber] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [callerentereddigits] [varchar](40) COLLATE Latin1_General_CI_AS NULL,
    [badcalltag] [char](1) COLLATE Latin1_General_CI_AS NULL,
    [transfer] [bit] NULL,
    [NextSeqNum] [smallint] NULL,
    [redirect] [bit] NULL,
    [conference] [bit] NULL,
    [flowout] [bit] NULL,
    [metservicelevel] [bit] NULL,
    [campaignid] [int] NULL,
    [origprotocolcallref] [varchar](32) COLLATE Latin1_General_CI_AS NULL,
    [destprotocolcallref] [varchar](32) COLLATE Latin1_General_CI_AS NULL,
    [convertedStartDatetimelocal] [datetime2](7) NULL,
    [convertedEndDatetimelocal] [datetime2](7) NULL,
    [AltKey]  AS (concat([sessionid],[sessionseqnum],[nodeid],[profileid]) collate database_default) PERSISTED NOT NULL,
    [PrvSeqNum] [smallint] NULL,
 CONSTRAINT [PK_contactcalldetail] PRIMARY KEY CLUSTERED 
(
    [sessionid] ASC,
    [sessionseqnum] ASC,
    [nodeid] ASC,
    [profileid] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
/****** Object:  Table [dbo].[contactqueuedetail]    Script Date: 1/10/2019 9:10:04 AM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[contactqueuedetail](
    [sessionid] [decimal](18, 0) NOT NULL,
    [sessionseqnum] [smallint] NOT NULL,
    [profileid] [int] NOT NULL,
    [nodeid] [smallint] NOT NULL,
    [targetid] [int] NOT NULL,
    [targettype] [smallint] NOT NULL,
    [targetTypeDescription] [varchar](10) COLLATE Latin1_General_CI_AS NULL,
    [qindex] [smallint] NOT NULL,
    [queueorder] [smallint] NOT NULL,
    [disposition] [smallint] NULL,
    [dispositionDescription] [varchar](50) COLLATE Latin1_General_CI_AS NULL,
    [metservicelevel] [bit] NULL,
    [queuetime] [smallint] NULL,
 CONSTRAINT [PK_contactqueuedetail] PRIMARY KEY CLUSTERED 
(
    [sessionid] ASC,
    [sessionseqnum] ASC,
    [profileid] ASC,
    [nodeid] ASC,
    [targetid] ASC,
    [targettype] ASC,
    [qindex] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
/****** Object:  Index [<Name of Missing Index, sysname,>]    Script Date: 1/10/2019 9:10:04 AM ******/
CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>] ON [dbo].[contactcalldetail]
(
    [convertedStartDatetimelocal] ASC
)
INCLUDE (   [sessionid],
    [sessionseqnum],
    [nodeid],
    [profileid]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
/****** Object:  Index [idx_CCD_ContactType_DestType_StDtLocal]    Script Date: 1/10/2019 9:10:04 AM ******/
CREATE NONCLUSTERED INDEX [idx_CCD_ContactType_DestType_StDtLocal] ON [dbo].[contactcalldetail]
(
    [destinationtype] ASC,
    [contacttype] ASC,
    [convertedStartDatetimelocal] ASC
)
INCLUDE (   [sessionid],
    [sessionseqnum],
    [nodeid],
    [profileid],
    [convertedEndDatetimelocal]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
SET ANSI_PADDING ON
GO
/****** Object:  Index [idx_CQD_Profile_Traget_TargetType]    Script Date: 1/10/2019 9:10:04 AM ******/
CREATE NONCLUSTERED INDEX [idx_CQD_Profile_Traget_TargetType] ON [dbo].[contactqueuedetail]
(
    [profileid] ASC,
    [targetid] ASC,
    [targettype] ASC
)
INCLUDE (   [targetTypeDescription],
    [queueorder],
    [disposition],
    [dispositionDescription],
    [queuetime]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO

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Answer 1

Pau*_*ite 11

隐式转换是由计算列引起的AltKey：

CREATE TABLE dbo.Test
(
    [sessionid] [decimal](18, 0) NOT NULL,
    [sessionseqnum] [smallint] NOT NULL,
    [nodeid] [smallint] NOT NULL,
    [profileid] [int] NOT NULL,
    [AltKey] AS 
        CONCAT
        (
            [sessionid],
            [sessionseqnum],
            [nodeid],
            [profileid]
        ) PERSISTED NOT NULL,
);

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鉴于上面的简化表，下面的简单语句生成与问题中给出的相同的隐式转换警告：

SELECT T.*
FROM dbo.Test AS T;

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从文档（强调）：

CONCAT 在连接之前将所有参数隐式转换为字符串类型。

当 SQL Server 考虑不使用持久值但显式计算值的计划替代方案时，会添加警告。如果最终计划使用持久值，则不会删除警告。

在这种情况下，可以安全地忽略警告。据我所知，这也适用于您的执行计划 - 涉及的隐式转换CONCAT不会对计划选择产生不利影响。

使用记录和支持的跟踪标志 176 可防止持久计算列扩展并删除警告：

SELECT * FROM dbo.Test AS T OPTION (QUERYTRACEON 176);
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有关更多详细信息，请参阅我的文章正确持久的计算列。

Answer 2

Jos*_*ell 5

这些是您收到隐式转换警告的字段：

[ccd].[profileid] (int 到 varchar(12))
[ccd].[nodeid] (smallint 到 varchar(6))
[ccd].[sessionseqnum] (smallint 到 varchar(6))
[ccd].[sessionid] （十进制到 varchar(41)）

引用的字段不是查询中任何参数/过滤器的一部分

当然，在您的加入条件中。这里是 ccd.profileid 用作过滤器的地方（以及与 agentconnectiondetail 的连接）：

FROM contactcalldetail ccd 
    INNER JOIN contactqueuedetail csqd 
        ON ccd.sessionID=csqd.sessionid 
            AND ccd.sessionSeqNum=csqd.sessionSeqNum 
            AND ccd.nodeID=csqd.nodeID 
            AND ccd.profileid=csqd.profileid -- Right here

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并且在所有涉及的表中，列数据类型都相同

您可能需要仔细检查表定义

contactcalldetail.profileid
contactqueuedetail.profileid
agentconnectiondetail .profileid

听起来他们没有使用您认为他们正在使用的数据类型。

它真的会影响基数估计吗？

根据您提供的信息，我的回答中有一些猜测。我鼓励您将实际的执行计划和表定义添加到您的问题中，以便我们了解可能会影响这些隐式转换问题的所有细节。

通常，连接条件的隐式转换会导致估计出现严重问题。在没有看到实际执行计划的情况下，很难说这是否发生在您的情况下。

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