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Stairway to SQL Server Indexes: Step 2, Deeper into Nonclustered Indexes


Stairway to SQL Server Indexes: Step 2, Deeper into Nonclustered Indexes

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David Durant
David Durant
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Comments posted to this topic are about the item Stairway to SQL Server Indexes: Step 2, Deeper into Nonclustered Indexes
russella0-96423
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I think the line that reads 'scanning the entire table of one million rows' should probably be 'scanning the entire table of twenty thousand odd rows'.

I'm not being pedantic here - I always like it when someone questions something in a doc I've written as it shows they've read it. The only reason I noticed it was such a good article that I was paying proper attention when I read it Smile.

Thanks for this series, I'm really enjoying it.

I'm meant to be a seasoned DBA, sometimes it worries me how rusty I am on some very fundamental subjects.

Best,

Andy



David Durant
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Andy,

Sorry for the long delay in replying; have been completing the remaining levels.

Will reread the level with an eye of rewording it.

Thanks for the input,
Dave Durant.
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GURSETHI
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Hi David,

One quick one. In session II of Stairway to SQL Server Indexes you mentioned that:

* Non Clustered Index Is a sorted set of entries.

I have little doubt on it.

If we run below query you will find that the output of first query on "CONTACTS_INDEX" table with "FULLNAME" index on "LastName, FirstName" the out put is not sorted.

SELECT * FROM DBO.CONTACTS_INDEX WHERE LASTNAME LIKE 'Ste%'

But when we run the below query on "CONTACT_NOINDEX" table results are sorted.

SELECT * FROM DBO.CONTACTS_NOINDEX WHERE LASTNAME LIKE 'Ste%'


So now my question is why is it so? If I do a select on Heap table I am getting data sorted but when I do a select on table with NonCluster index data is not sorted.
mirzafarazbeg
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Dave,

Really benefiting from this series, in fact, all stairway series.

I have a very beginner-level question, you're showing the contents of the indexes as if selecting from a table. Is there a way to actually do it. I mean like "select * from ix_table1_nc_index"... is there a way to do that?

Thanks,
Faraz
Uwe Ricken
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Hi Faraz,

you can use DBCC IND if you use SQL Server < 2012 or sys.dm_db_database_page_allocation for SQL Server >= 2012.
This will give you a list of allocated pages.
To have a look at the root node (or any other page of the index you use

DBCC PAGE

More details about can be found here:
http://blogs.msdn.com/b/sqlserverstorageengine/archive/2006/12/13/more-undocumented-fun_3a00_-dbcc-ind_2c00_-dbcc-page_2c00_-and-off_2d00_row-columns.aspx

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Phil Parkin
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Uwe Ricken (11/26/2014)
Hi Faraz,

you can use DBCC IND if you use SQL Server < 2012 or sys.dm_db_database_page_allocation for SQL Server >= 2012.
This will give you a list of allocated pages.
To have a look at the root node (or any other page of the index you use

DBCC PAGE

More details about can be found here:
http://blogs.msdn.com/b/sqlserverstorageengine/archive/2006/12/13/more-undocumented-fun_3a00_-dbcc-ind_2c00_-dbcc-page_2c00_-and-off_2d00_row-columns.aspx


Helpful as this response may be, it does not answer Faraz' question.


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Uwe Ricken
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Hey Phil,

why doesn't it meet the requirements / question?
He wants to have the content of the index itself or do I missunderstand the request?


CREATE TABLE dbo.foo
(
id INT NOT NULL,
c1 CHAR(20) NOT NULL,
c2 DATE NOT NULL,

CONSTRAINT pk_foo_id PRIMARY KEY CLUSTERED (Id)
);
GO

INSERT INTO dbo.foo (id, c1, c2) VALUES
(1, 'col1', '20140101'),
(2, 'col2', '20140201'),
(3, 'col3', '20140301'),
(4, 'col4', '20140401')
GO

CREATE NONCLUSTERED INDEX ix_foo_c2 ON dbo.foo(c2);
GO

-- check the index id's of dbo.foo
SELECT * FROM sys.indexes WHERE object_id = OBJECT_ID('dbo.foo');
GO

-- IF nonclustered index is ID = 2
DBCC IND('demo', 'dbo.foo', 2);

-- Output of page content to client
-- after execution of DBCC IND the page with type = 2 is
-- the index page! 10 is IAM!
-- Replace the page_id with that evaluated id
DBCC TRACEON (3604);
DBCC PAGE('demo', 1, <page_id, 3);
GO



When running this script you get the list of values from one page of the index with its content!
BTW: The question was from 2012 Smile
Seems to be worthless to discuss the intention Smile

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MVP - Data Platform (2013 - ...)
my blog: http://www.sqlmaster.de (german only!)
Phil Parkin
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why doesn't it meet the requirements / question?
He wants to have the content of the index itself or do I missunderstand the request?


Because I believe the poster was asking whether the actual physical data could be returned by selecting from the index, not the index meta data.


Help us to help you. For better, quicker and more-focused answers to your questions, consider following the advice in this link.

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Iwas Bornready
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What this article has done is show me how much index study I need to do. Thanks.
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