Question

根据相同列的不同条件创建多个筛选索引是否有意义？例如，假设如下：

 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

或者创建一个非过滤索引会更好吗？

如果进行以下查询SELECT * FROM Skills WHERE SkillLevel BETWEEN 7 AND 1会发生什么？

Answer 1

除非每个技能等级变化都有数百万条记录。

即，
在5和3之间在5和7之间

我不建议这样做，我建议创建一个单独的过滤索引，如下所示

skilllevel between 1 and 10

如果进行以下查询会发生什么SELECT * FROM Skills WHERE SkillLevel BETWEEN 7 AND 1？

如果你的select *包含许多列，而不是索引中没有指定的列，则sql可能

选择使用此索引，并在基表上查找其余列
进行全表扫描

我会创建一个以下覆盖索引，但这取决于您的数据

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

我做了一些测试以了解更多，你可以在下面找到测试脚本

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

现在让我们运行一些查询

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

然而，即使你在技能水平之间有数百万行，我也不推荐这些指数。我会建议分配

同一列的多个筛选索引

1 个答案: