同一列的多個過濾索引

Question

根據不同條件爲同一列創建多個過濾索引是否合理？例如，假設以下內容：

CREATE TABLE [dbo].[Skills](
    [UserId] INT NOT NULL PRIMARY KEY, 
    [SkillTitle] NVARCHAR(50) NOT NULL, 
    [SkillLevel] INT NOT NULL CHECK ([SkillLevel] BETWEEN 0 AND 10) 
) 
GO 

CREATE INDEX [IX_Skill_Low] ON [dbo].[Skill] (SkillTitle,SkillLevel) WHERE SkillLevel BETWEEN 3 AND 0 
GO 

CREATE INDEX [IX_Skill_Moderate] ON [dbo].[Skill] (SkillTitle,SkillLevel) WHERE SkillLevel BETWEEN 5 AND 3 
GO 

CREATE INDEX [IX_Skill_Good] ON [dbo].[Skill] (SkillTitle,SkillLevel) WHERE SkillLevel BETWEEN 7 AND 5 
GO 

CREATE INDEX [IX_Skill_High] ON [dbo].[Skill] (SkillTitle,SkillLevel) WHERE SkillLevel > 7 

或者創建單個非過濾索引會更好嗎？

如果進行以下查詢，會發生什麼SELECT * FROM Skills WHERE SkillLevel BETWEEN 7 AND 1？

Answer 1

除非您有數百萬記錄用於每種技能等級的變化。

即，
在5至7

在5和3
我不會建議，我建議建立像下面

skilllevel between 1 and 10 

是怎樣的一個單一過濾指數如果進行以下查詢，則會發生SELECT * FROM技能WHERE SkillLevel BETWEEN 7 AND 1？

如果如果你select *包含許多列以外，其在指數沒有specfied，SQL可能

• 選擇使用該索引和做基表查找的列的其餘
• 做一個全表掃描

我會創造一個下方覆蓋指數，但是這取決於你的數據

create index nci_test on table(skilllevel) 
include(SkillTitle) 

我做了一些測試，以瞭解更多，你可以找到下面的測試腳本

CREATE TABLE [dbo].[Skills](
    [UserId] INT NOT NULL identity(1,1) PRIMARY KEY, 
    [SkillTitle] NVARCHAR(50) NOT NULL, 
    [SkillLevel] INT NOT NULL CHECK ([SkillLevel] BETWEEN 0 AND 10) 
) 
GO 

insert into dbo.Skills 
(SkillTitle,SkillLevel) 
select cast(NEWID() as varchar(50)), 
case when rand()*10<0 then 1 else rand()*10 end 
go 100000 

現在讓我們運行一些查詢

create index nci_1and5 on dbo.skills(skilllevel) 
include(skilltitle) 
where skilllevel >= 1 and skilllevel <=5 

create index nci_5and10 on dbo.skills(skilllevel) 
include(skilltitle) 
where skilllevel >5 and skilllevel <=10 

select * from skills where skilllevel 
between 1 and 4--uses 1 to 5 index 

select * from skills where skilllevel 
between 6 and 10--uses 6 to 10 index 

select * from skills where skilllevel 
between 1 and 7--uses scan 

但是我不推薦這些指標，即使你有百萬行之間的技能levels.I將建議分區