Could You please explain, why clustered indexes should be used on columns with low selectivity?
If I have a table with unique, identity column, where I keep for exemple a transaction number, I thought that clustered
index is the best for it. Each line is just put after the other one.
And if I have an index with low selectivity, and I want to do some insert / update / delete operations on that table, won’t it take more time
to do these operations?
I’am a little bit confused now …
Thank’s in advance!
Ewelina

Hi i am curious to know what is the difference between

CREATE INDEX PIndex ON Persons (LastName) ,
CREATE INDEX PIndex ON Persons (DOB)

AND

CREATE INDEX PIndex ON Persons (LastName,DOB)

You mention that Clustered Index “Physically rearranges the data in the table to conform to the index constraints”.

However, as per Brad McGehee’s Blog & the MCTS Self-paced training kit from Microsoft 70-431, it is not the case.

The rows in a clustered table are logically ordered by the key selected for the clustered index.

Refer “Types of Indexes” and “Clustered” section in the below blog for clarity:
http://www.simple-talk.com/sql/database-administration/brads-sure-guide-to-indexes/

I believe it can be modified as “Physically rearranges all the data pages that contain every row in the entire table.”

I also see that it is mentioned in detail in the next paragraph correctly, however, correcting the above would make it clear for everyone.

Please help me understand if I am interpreting your statement incorrectly.

Thanks in advance!

Thanks,
Adarsh

create CLUSTERED index inddex_as
on Authors(phone)

I want to Alter As

alter CLUSTERED index inddex_as
on Authors(phone,author_id)

Please Help me…

Thanks …

Primary Key by default creates a Clustered Index, but it is not mandatory to link both of them.

It means, you can have Clustered Index on a non Primary Key Column as well. If you create Clustered Index on a Non-Primary Key column, which has duplicates, SQL Server can still Creates Clustered Index on that column by making it unique internally. It adds Unique Numbers to the Non- Primary Key Column which makes that column Unique and then creates an Index on it, because this is internal to SQl Server, we cannot see it in SSMS.

Be very sure, to test out before deploying this to production. Choose wisely which column(s) to pick up for Clustered Index.

~ IM.

We have a SQL Server 2008 R2 databases and don’t use a PK & hence no CLUSTERED Index on the table.

We have only Non Clustered Indexes as part of our design.

So just wanted to know whether there is an alternative to Reorganize of Indexes for the HEAP Structures.

If Yes then how this needs to be done?

can you explain the difference between Key column and fields. Because as an advantage of included index you said the 16 key column and index size 900 bytes. But you also said the we can include 1023 fields.. I am confused.

if you run sp_help {tablename}
or sp_helpindex {tablename}
is only tells you what columns make up the index, not which columns are also included

But the one with the primary key becomes the column to which by default the Clustered indexes is created.

1.what and how many type of indexing in SQL server???
i found 3 type that as i understand on your articles
1-Clustered Index

2-Non-Clustered Index

3-Included Column Index (New in SQL Server 2005)

another questions
2.What the different of indexing between the SQLserver 2005 and SQL server 2008??

3.What the differnt of INDEXING on microsoft SQL sever and Oracle DB ??

please bear with me sir.
thank you so much for your site. AND that help me.
m getting lot of hepl from this site.

My guess is that in 90% of cases you don’t have to think about paging and if you do, hire a consultant :)

2) Key columns and non-key columns. Let’s consider the following SQL statement:

CREATE NONCLUSTERED INDEX [IX_Foo] ON [dbo].[Table]
( Column1, Column2)
INCLUDE (Column3, Column4)

This is called covering composite index (I think). Key columns are Column1 and Column2. They can be used, for example, as part of WHERE and JOIN clauses.

Non-key columns are Column3 and Column4. They can be used in SELECT fields. So for example:

SELECT Column3, Column4 FROM [dbo].[Table] WHERE Column1 = 1 AND Column2 = 2

Thanks for your prompt response.
I need to understand the following thing:

1) What will the data pages contains and how it appears?

2) What is meant by Key and non key columns.

3) Is there any diagramatic explanation on index topic.

Please share the answers for the above questions.

Regards
Denison.s

A heap is a table without a clustered index. read more at the below BOL link:

ms-help://MS.SQLCC.v9/MS.SQLSVR.v9.en/udb9/html/72f63db6-7306-4c43-a73d-7eaa4ffe1f82.htm

Note: you will need to paste this link in BOL.
Start>Programs>Microsoft SQl Server 2005>Documentation and Tutorials> SQL Server Books Online

CREATE TABLE ORDER1 (
order_id bigint NOT NULL,
product_id int NOT NULL,
order_date datetime NOT NULL,
price decimal(21,2) NOT NULL,
PRIMARY KEY (order_id, product_id, order_date)
)

alter table Order1 drop constraint

actually wirite this syntax drop constraint and constraint name but above samplee how to identify the constraint name

alter table employee drop constraint id_pkey