在 exists 语句中不使用索引的查询

Question

我在下面的 table dbo.tbl_SpeedRun 上有索引 IDX_tbl_SpeedRun_StatusTypeID_GameID_CategoryID_LevelID_PlusInclude。下面查询中的 exists 语句需要一段时间 (1m 10s) 表示 [dbo].[tbl_SpeedRun] ([StatusTypeID],[LevelID]).

上缺少索引

为什么 exists 语句没有使用我创建的索引？它已经包含列 [StatusTypeID],[LevelID].

Table:

CREATE TABLE [dbo].[tbl_SpeedRun] 
( 
    [OrderValue] [int] NOT NULL IDENTITY(1,1),
    [ID] [varchar] (50) NOT NULL, 
    [StatusTypeID] [int] NOT NULL,
    [GameID] [varchar] (50) NOT NULL,
    [CategoryID] [varchar] (50) NOT NULL,
    [LevelID] [varchar] (50) NULL,
    [SubCategoryVariableValues] [varchar] (1000) NULL,
    [PlayerIDs] [varchar] (1000) NULL,
    [PlatformID] [varchar] (50) NULL,
    [RegionID] [varchar] (50) NULL,
    [IsEmulated] [bit] NOT NULL,
    [Rank] [int] NULL,
    [PrimaryTime] [bigint] NULL,
    [RealTime] [bigint] NULL,
    [RealTimeWithoutLoads] [bigint] NULL,
    [GameTime] [bigint] NULL,
    [Comment] [varchar] (MAX) NULL,
    [ExaminerUserID] [varchar] (50) NULL, 
    [RejectReason] [varchar] (MAX) NULL, 
    [SpeedRunComUrl] [varchar] (2000) NOT NULL,
    [SplitsUrl] [varchar] (2000) NULL,
    [RunDate] [datetime] NULL,  
    [DateSubmitted] [datetime] NULL,   
    [VerifyDate] [datetime] NULL,   
    [ImportedDate] [datetime] NOT NULL CONSTRAINT [DF_tbl_SpeedRun_ImportedDate] DEFAULT(GETDATE()),
    [ModifiedDate] [datetime] NULL
) ON [PRIMARY] 
GO 

ALTER TABLE [dbo].[tbl_SpeedRun] 
    ADD CONSTRAINT [PK_tbl_SpeedRun] 
        PRIMARY KEY NONCLUSTERED ([ID]) WITH (FILLFACTOR=90) ON [PRIMARY] 
GO

CREATE CLUSTERED INDEX [IDX_tbl_SpeedRun_OrderValue] 
    ON [dbo].[tbl_SpeedRun] ([OrderValue]) WITH (FILLFACTOR=90) ON [PRIMARY] 
GO

CREATE NONCLUSTERED INDEX [IDX_tbl_SpeedRun_StatusTypeID_GameID_CategoryID_LevelID_PlusInclude] 
    ON [dbo].[tbl_SpeedRun] ([StatusTypeID], [GameID], [CategoryID],[LevelID]) 
       INCLUDE ([SubCategoryVariableValues], [PlayerIDs], [Rank],[PrimaryTime])
GO

查询：

SELECT 
    CASE 
       WHEN EXISTS (SELECT 1 FROM dbo.tbl_SpeedRun rn WITH (NOLOCK) 
                    WHERE rn.LevelID = l.ID AND rn.StatusTypeID = 1) 
          THEN 1 
          ELSE 0 
    END
FROM
    dbo.tbl_Level l WITH (NOLOCK)
WHERE 
    l.GameID = 'pd0wq901'
ORDER BY 
    l.OrderValue

Answer 1

这是子查询的 from 子句：

WHERE rn.LevelID = l.ID AND rn.StatusTypeID = 1

此谓词的有用索引将以任意顺序涉及两列。

您现有的索引不满足该要求。它有列：

[StatusTypeID], [GameID], [CategoryID], [LevelID]) 
INCLUDE ([SubCategoryVariableValues], [PlayerIDs], [Rank], [PrimaryTime])

两列都在这里，但隐藏在其他列中 - 因此数据库无法利用它来加速子查询。

底线：默认情况下，创建涉及大量列的大型索引不会加快查询速度。相反，您可以单独分析每个查询并定义适当的优化。

在 exists 语句中不使用索引的查询

Query not using index in exists statement

sql

tsql

sql-server

subquery

query-optimization