Very clear and informative. Understanding tuning is tricky but this post made it seem simple.

My question is, when creating the composite index, why do you specify city first, rather than ID, which is more unique.

Thanks,
Steven

Nice explanation, too easy to understand.

i have one question over here, let me write your code what you have used.

SELECT ID, FirstName
FROM OneIndex
WHERE City = ‘Las Vegas’

CREATE NONCLUSTERED INDEX [IX_OneIndex_Include] ON [dbo].[OneIndex]
(
City
) INCLUDE (FirstName,ID) ON [PRIMARY]
GO

As i can see in above code, you are selecting ID then FirstName columns in Select list, but while including these columns for Non Clustered Index you have not followed the same sequence/order (Included Firstname then ID)

Is this really fruitful to improve query performance?

As per my understanding, we should follow the same sequence as we are selecting the fields, same sequence should be followed while including in Index, It would be easy for SQL Server to get the data in fast way.

Regards,
Girijesh

Thanks for this post.Its very easy to understand.Good post.

I’m confused why the best recommendation isn’t to create a clustered index. In our situation we have a 5 Billion row table without a clustered index. The RID lookups are killing us. The need for a lot of extra non-clustered indexes is also killing performance because this is on a replication server.

Finally the writes to a clustered index are dramatically less than to a non-clustered index with a HEAP.

See: http://msdn.microsoft.com/en-us/library/cc917672.aspx#EFAA

How can anyone justify a large table without a clustered index?

Nick

Nice post, very impressive and understandable…Thank You.

We have a requirement to Merge six 12millions data tables into single Table.All the tables are having duplicate Emails.So We put the Primary key for email column using EnterPrise Manager and We r trying to merge by writing the following insert query, But it’s taking more than 20hrs…:-(

Insert into Total( Email,FirstName,LastName,Address,City,State,Zipcode,Gender,DOB ,
Phone,WebAddress1,Webaddress2,IPAddress,DateTime,Interest )
Select Email,FirstName,LastName,Address,City,State,Zipcode,Gender,DOB ,
Phone,WebAddress1,Webaddress2,IPAddress,DateTime,Interest
From [Set4]
Where
(not exists(select email from Total
where Total.email=[Set4].email))

How can we do this most efficiently??? Please Help Us……

Thanks in advance…

Please read my follow up post here :
SQL SERVER – Query Optimization – Remove Bookmark Lookup – Remove RID Lookup – Remove Key Lookup – Part 3
http://blog.sqlauthority.com/2009/10/12/sql-server-query-optimization-remove-bookmark-lookup-remove-rid-lookup-remove-key-lookup-part-3

Kind Regards,
Pinal

I’m curious to know why you have included the ID column in the covering index, as well as in the nc index with the includes. I thought all columns in the Clustered index were already included in the non clustered index.

Is there a reason why you did that?

Thanks,

If we do not need those columns in query for SURE they need to be removed. I agree with you there.

I will send you other details soon.

Kind Regards,
Pinal