インデックス作成とそれらの違いについて多くのことを読みました。現在、プロジェクトでクエリの最適化に取り組んでいます。クエリの実行時に使用する必要がある非クラスター化インデックスを作成しましたが、そうではありません。以下の詳細:
テーブル：
索引：
CREATE NONCLUSTERED INDEX [_IXProcedure_Deleted_Date] ON [por].[DailyAsset]
(
[Deleted] ASC,
[Date] DESC
)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
Entity Framework によって生成されたクエリ:
exec sp_executesql N'SELECT
[Project1].[C1] AS [C1],
[Project1].[AssetId] AS [AssetId],
[Project1].[Active] AS [Active],
[Project1].[Date] AS [Date]
FROM ( SELECT
[Extent1].[AssetId] AS [AssetId],
[Extent1].[Active] AS [Active],
[Extent1].[Date] AS [Date],
1 AS [C1]
FROM [por].[DailyAsset] AS [Extent1]
WHERE (0 = [Extent1].[Deleted]) AND ([Extent1].[Date] < @p__linq__0)
) AS [Project1]
ORDER BY [Project1].[Date] DESC',N'@p__linq__0 datetime2(7)',@p__linq__0='2014-05-01 00:00:00'
実行計画：
インデックスの詳細がありません:
The Query Processor estimates that implementing the following index could improve the query cost by 23.8027%.
CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>]
ON [por].[DailyAsset] ([Deleted],[Date])
INCLUDE ([AssetId],[Active])
インデックスに AssetId と Active 列を含めると、インデックスが使用されることを認識しています。
では、列を含めないと機能しないのはなぜですか?
これは、結果としてすべての列がフェッチされる別のクエリの簡単な例です。(強制) インデックス シークの使用に対する唯一の解決策は、同じ推定サブツリー コストを持つインデックスにすべての列を含めることです (明らか)。
ここでのもう 1 つの厄介な問題は、Sort の無知です。日付列はインデックスにあり、DESCENDING に設定されています。それは完全に無視されます。もちろん、Sort 操作は実行計画で高価な場所を占めます。
更新 1:
@Jayachandran が指摘したように、上記のクエリでは IndexSeek + KeyLookUp を使用する必要がありますが、インデックスのカバーは十分に文書化されており、AssetId および Active 列を含める必要があると想定しています。私はそれに同意します。
以下のクエリでカバリング インデックスの有用性を示すために、UPDATE 1 を作成しています。同じテーブル、より大きな結果セット。私が理解できる限り、単一の列をインデックスで使用しないでください。インデックスは、日付および削除された列に対して作成されたままです。
exec sp_executesql N'SELECT
[Project1].[DailyAssetId] AS [DailyAssetId],
[Project1].[AssetId] AS [AssetId],
[Project1].[CreatedByUserId] AS [CreatedByUserId],
[Project1].[UpdatedByUserId] AS [UpdatedByUserId],
[Project1].[TimeCreated] AS [TimeCreated],
[Project1].[TimeUpdated] AS [TimeUpdated],
[Project1].[Deleted] AS [Deleted],
[Project1].[TimeDeleted] AS [TimeDeleted],
[Project1].[DeletedByUserId] AS [DeletedByUserId],
[Project1].[Active] AS [Active],
[Project1].[Date] AS [Date],
[Project1].[Quantity] AS [Quantity],
[Project1].[TotalBookValue] AS [TotalBookValue],
[Project1].[CostPrice] AS [CostPrice],
[Project1].[CostValue] AS [CostValue],
[Project1].[FairPrice] AS [FairPrice],
[Project1].[FairValue] AS [FairValue],
[Project1].[UnsettledQuantity] AS [UnsettledQuantity],
[Project1].[UnsettledValue] AS [UnsettledValue],
[Project1].[SettlementDate] AS [SettlementDate],
[Project1].[EffectiveDate] AS [EffectiveDate],
[Project1].[PortfolioId] AS [PortfolioId]
FROM ( SELECT
[Extent1].[DailyAssetId] AS [DailyAssetId],
[Extent1].[AssetId] AS [AssetId],
[Extent1].[CreatedByUserId] AS [CreatedByUserId],
[Extent1].[UpdatedByUserId] AS [UpdatedByUserId],
[Extent1].[TimeCreated] AS [TimeCreated],
[Extent1].[TimeUpdated] AS [TimeUpdated],
[Extent1].[Deleted] AS [Deleted],
[Extent1].[TimeDeleted] AS [TimeDeleted],
[Extent1].[DeletedByUserId] AS [DeletedByUserId],
[Extent1].[Active] AS [Active],
[Extent1].[Date] AS [Date],
[Extent1].[Quantity] AS [Quantity],
[Extent1].[TotalBookValue] AS [TotalBookValue],
[Extent1].[CostPrice] AS [CostPrice],
[Extent1].[CostValue] AS [CostValue],
[Extent1].[FairPrice] AS [FairPrice],
[Extent1].[FairValue] AS [FairValue],
[Extent1].[UnsettledQuantity] AS [UnsettledQuantity],
[Extent1].[UnsettledValue] AS [UnsettledValue],
[Extent1].[SettlementDate] AS [SettlementDate],
[Extent1].[EffectiveDate] AS [EffectiveDate],
[Extent1].[PortfolioId] AS [PortfolioId]
FROM [por].[DailyAsset] AS [Extent1]
WHERE (0 = [Extent1].[Deleted]) AND ([Extent1].[Date] < @p__linq__0)
) AS [Project1]
ORDER BY [Project1].[Date] DESC',N'@p__linq__0 datetime2(7)',@p__linq__0='2014-05-01 00:00:00'