asked on

indexed views not being used by optimizer

Please run the code below in a scratch database. On the last query, check the execution plan. Why does it do a full table scan instead of doing an index seek on the covering index of the view?

The goal is to do a case-insensitive search on the LastName column, which in my real base table is collation Latin1_General_BIN (the server default here), by way of an index seek, not a scan. I thought I could do this by creating a view of the table and setting the collation on that field to SQL_Latin1_General_CP1_CI_AS in the view, and index this version of the column on the view.

Thanks

create table dbo.tTest(id int identity(1,1), LastName varchar(80) COLLATE Latin1_General_BIN, FirstName varchar(80) COLLATE Latin1_General_BIN) 
GO

create unique clustered index tx0 on dbo.tTest(id)
GO

insert into dbo.tTest select 'Doe','John'
insert into dbo.tTest select 'Doe','Jane'
insert into dbo.tTest select 'Bach','Hellen'
insert into dbo.tTest select 'Smith','Jane'
insert into dbo.tTest select 'Smith','Mike'
insert into dbo.tTest select 'Jones','Mike'
GO

create view dbo.vTest  WITH SCHEMABINDING  as
select id, (LastName COLLATE SQL_Latin1_General_CP1_CI_AS) as LastName, (FirstName COLLATE SQL_Latin1_General_CP1_CI_AS) as FirstName
from dbo.tTest
GO

create unique clustered index vx0 on dbo.vTest(id) 
GO

create unique index vx1 on dbo.vTest(LastName,FirstName,id)
GO

select id, FirstName, LastName
from dbo.vTest -- with (index=vx1)
where LastName  = 'BACH'  
GO

--  drop view dbo.vTest
--  truncate table dbo.tTest
--  drop table dbo.tTest
GO

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knightEknight

ASKER

FYI - I can achieve the overall goal by creating calculated fields on the base table instead of a view (see below), but I would rather get this to work in a view:

use staging
GO

create table dbo.tTest(
                        id int identity(1,1), 
                        LastName  varchar(80) COLLATE Latin1_General_BIN, 
                        FirstName varchar(80) COLLATE Latin1_General_BIN,
                        cLastName  as (LastName  COLLATE SQL_Latin1_General_CP1_CI_AS),
                        cFirstName as (FirstName COLLATE SQL_Latin1_General_CP1_CI_AS)
                      ) 
GO

create unique clustered index tx0 on dbo.tTest(id)
GO

insert into dbo.tTest select 'Doe','John'
insert into dbo.tTest select 'Doe','Jane'
insert into dbo.tTest select 'Bach','Hellen'
insert into dbo.tTest select 'Smith','Jane'
insert into dbo.tTest select 'Smith','Mike'
insert into dbo.tTest select 'Jones','Mike'
GO

create unique index tx1 on dbo.tTest(cLastName,cFirstName,id)
GO

select id, cFirstName, cLastName
from dbo.tTest
where cLastName  = 'BACH'

--  drop view dbo.vTest
--  truncate table dbo.tTest
--  drop table dbo.tTest

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knightEknight

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knightEknight

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