Query not using index in exists statement - sql

Question

I have the index IDX_tbl_SpeedRun_StatusTypeID_GameID_CategoryID_LevelID_PlusInclude on table dbo.tbl_SpeedRun below. The exists statement in the query below is taking a while (1m 10s) saying there is a missing index ON [dbo].[tbl_SpeedRun] ([StatusTypeID],[LevelID]).
Why is the exists statement not using the index I created? It already includes the columns [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
Query:
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

This is the from clause of your subquery:
WHERE rn.LevelID = l.ID AND rn.StatusTypeID = 1
A helpful index for this predicate would involve the two columns, in any order.
Your existing index does not satisfy that requirement. It has columns:
[StatusTypeID], [GameID], [CategoryID], [LevelID])
INCLUDE ([SubCategoryVariableValues], [PlayerIDs], [Rank], [PrimaryTime])
Both columns are here, but buried within others - so the database cannot take advantage of it to speed up the subquery.
Bottom line: creating a large index that involves a lot of columns does not speed up queries by default. Instead, you can analyze each query individually and define the proper optimization.