Covering Indexes
Aug 1, 2006
Hi,
I asked the similar question before but I have again some doubts about covering indexes.
Besides, tomorrow I have a Microsoft MCAD 70-229 exam so please help me.
In here,
SELECT * FROM Order WHERE OrderID > 12 ORDER BY OrderDate
we create composite nonclustered index for both OrderID and OrderDate column.
Leftmost is OrderID.
So
when our first research is happening(Where clause), the only
nonclustered index which is used is OrderID index. And then, when we
pass through the second search(ORDER BY clause), OrderDate index become activated.
So
we can say that the seleection of indexes in composite indexes is
determined according to the situation of the query at that time.
Hence, is this all correct ?
Best wishes,
Mert
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Mar 12, 2008
I plan to use covering indexes as my core tables are really huge. I wanted to check if the new feature "Included Columns" for an index is beneficial in the following scenario:
If I have a non-clustered index within the limitations of 16 fields and under 900 bytes as opposed to having 1 field with 15 included fields for the same - what is the difference in performance? Is there any advantage in using the included columns?
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Apr 2, 2007
Hi,
Trying to optimize a query but not sure what to do. I have this query on which I ran an exec plan,
SET NOCOUNT ON;
SELECT qaTestSuite.TestSuiteID, qaTestSuite.TestSuiteStart, qaTestSuite.TestInterface, qaTestSuite.TestVersion, qaTests.TestMachine, qaTestSuite.TestClientMachine, qaTests.TestLogin, qaTests.TestLabel,
qaTestSuite.TestCLPs, qaTestSuite.TestSuiteEnd, qaTests.TestID, qaTests.TestIDInternal, qaTests.TestStart,
qaTests.TestName, qaTests.TestTier, qaTests.TestNo, qaTests.TestWFBCalled, qaTests.TestWFBTime,
qaTests.TestSearches, qaTests.TestSearchesTime, qaTests.TestResult, qaTests.TestEnd, qaTestMssgs.TestMssgsID,
qaTestMssgs.TestMssgTime, qaTestMssgs.TestMssgType, qaTestMssgs.TestMessage, qaTestSuite.TestMode
FROM qaTestSuite with(NOLOCK) INNER JOIN
qaTests with(NOLOCK) ON qaTestSuite.TestSuiteID = qaTests.TestSuiteID INNER JOIN
qaTestMssgs with(NOLOCK) ON qaTests.TestID = qaTestMssgs.TestID
order by qaTestSuite.TestSuiteStart DESC
and it gives me the following results:
Use a Bookmark (RID or Clustering Key) to look up the corresponding row in the Table or Clustered Index.
Physical Op: Bookmark Lookup
Logical Op: Bookmark Lookup
Est. Row Count: 128
Est. Row Size: 4760
Est. I/O Cost: 0.368
Est. CPU Cost: 0.000141
Est. Execs: 1.0
Est. Cost: 0.368888(89%)
Est. Subtree Cost:.415
Argument:
BOOKMARK:([Bmk1004]), OBJECT:([QAMaster].[dbo].[qaTestMssgs]) WITH PREFETCH
I have no idea what to do with that. Anyone have any clues? What I found online was that I should make a Covering Index, but I didn't find
any patterns on how to do that. Any one have ideas of how to do this?
Thanks very much for your help!
--PhB
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May 15, 2008
I have a table there is a query which has bad performance. This query normally can not use index because a lot of 'IS NULL','OR','LIKE' USED in where clause. I want to create a covering index for this query so it can use index scan only rather than Processor had to look up the row columns it needs
from a table or a clustered index.
current there are two index apply on that table:
CREATE UNIQUE CLUSTERED INDEX [Person_RecordID_UIX] ON Person
(
[RecordID] ASC
)
go
ALTER TABLE [Person] ADD CONSTRAINT Person_PK PRIMARY KEY NONCLUSTERED
(
[EntityID] ASC
)
How to add a covering index for the columns such as familyName,givenName, dob. All of these columns are not too much high selective.
Can I do like the following :
--create third index
CREATE NONCLUSTERED INDEX [Person_Cover_IX] ON [dbo].[Person]
(
[EntityID] ASC
)
INCLUDE ( [FamName],
[FirstName],
[DOB],
[Gender]
)
Or DROP Current index on entityid and recreate it with include clause.
What's the different between these two.
Thank you.
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Dec 5, 2007
Hello,
i have a database with about 300.000 entries. The database gets about 30 new entries every day. The Database has an FulltextIndex on several columns. This FulltextIndex will be updated every night.
But now i have found out, that the fulltextsearch doesn't work anymore for all entries that where added after April 2006.
When i for example make following sql-statementSELECT id,date FROM MyTable WHERE (CONTAINS((columnA),' "mykeyword" '))
i only get results that have a date after April 2006 (although there are matching entries after that date).
What can the reason for that be?
According to Management Studio the last Update of the FulltextCatalog has been made on 1st of December 2007. Everything looks normal and I didn't find any logs that are saying that there has been any errors.
Where do I have to look to be sure if the FullTextIndex does work?
Specs:
SQL Server 2005
Microsoft SQL Server Management Studio 9.00.1399.00Microsoft Analysis Services-Clienttools 2005.090.1399.00Microsoft Data Access Components (MDAC) 2000.086.3959.00 (srv03_sp2_rtm.070216-1710)Microsoft MSXML 2.6 3.0 6.0 Microsoft Internet Explorer 6.0.3790.3959Microsoft .NET Framework 2.0.50727.832Operating System 5.2.3790
greetings
Klaus
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Jan 2, 2015
I have created a covering Index like below,
----------------------------------------------------------------
CREATE NONCLUSTERED INDEX [INX_NONCLUS_COVERING_INVBAK] ON [dbo].[Invoices_Bak]
(
[SellerID] ASC, -- Key column
[BuyerID] ASC -- Key column
)
INCLUDE (
[ReceivedDate], --Non key column
[Code] ....
Above index has created on production environment, Now i would like alter above index that is from non key column to key column
You can find a non key column called [ReceivedDate] that is available in include part, i need to make this column to Key column.
How to do this proper way without affect production environment that is using unwanted disk size and more..
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Jan 16, 2008
I am working with a dynamically populated multi value parameter drop down list. In the case where there is only one value in the list, the horizontal scroll bar (due to the length of the value) covers up the first, and in this case only choice. The users cannot see it. This problem is only when running in report manager. It works ok in Visual Studio.
As a work around, I can add a dummy row, which then at least the users can see one row of data and then scroll down but, I would rather not do that, if there is another solution. Another option would be to set the default on the parameter so it is automatically selected but, in the case where there are many values, I do not want a default set.
Your help would be greatly appreciated.
Thanks!
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Aug 9, 2006
Hi,
When I create a unique constraint, SQL Server automatically creates an index on this constraint. So when I run the following...
ALTER TABLE PersonsProjects
WITH NOCHECK ADD CONSTRAINT NoDupes UNIQUE NONCLUSTERED (PersonID, ProjectID)
...SQL Server will create a composite index on PersonsProjects called NoDupes on PersonIDand ProjectID. Thing is, I need this index to include a third column Status since most queries use this column in conjunction with PersonID and ProjectID. If there was no index on this table, I would have created it as follows:
CREATE UNIQUE INDEX NoDupes ON PersonsProjects (PersonID, ProjectID) INCLUDE (Status) WITH IGNORE_DUP_KEY
But this won't enforce the unique constraint on PersonID and ProjectID when performing inserts and updates. Is there any way of creating a unique constraint with an included column?
I would rather not have two indexes...
NoDupes: PersonID,ProjectID
New Index: PersonID,ProjectID INCLUDE Status
...so I'm trying to determine what other options that might be available...please advise.
Thanks much.
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Jul 1, 2014
I'm working to improve performance on a database I've inherited, and there are several thousand indexes. I've got a list of ones which should definitely exist within the database, and I'm looking to strip out all the others and start fresh, though this list is still quite large (1000 or so).
Is there a way I can remove all the indexes that are not in my list without too much trouble? I.e. without having to manually go through them all individually. The list is currently in a csv file.
I'm looking to either automate the removal of indexes not in the list, or possibly to generate the Create statements for the indexes on the list and simply remove all indexes and then run these statements.
As an aside, when trying to list all indexes in the database, I've found various scripts to do this, but found they all seem to produce differing results. What is the best script to list all indexes?
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Sep 18, 2007
So I'm reading http://www.sql-server-performance.com/tips/clustered_indexes_p2.aspx and I come across this:
When selecting a column to base your clustered index on, try to avoid columns that are frequently updated. Every time that a column used for a clustered index is modified, all of the non-clustered indexes must also be updated, creating additional overhead. [6.5, 7.0, 2000, 2005] Updated 3-5-2004
Does this mean if I have say a table called Item with a clustered index on a column in it called itemaddeddate, and several non-clustered indexes associated with that table, that if a record gets modified and it's itemaddeddate value changes, that ALL my indexes on that table will get rebuilt? Or is it referring to the table structure changing?
If so does this "pseudocode" example also cause this to occur:
sqlstring="select * from item where itemid=12345"
rs.open sqlstring, etc, etc, etc
rs.Fields("ItemName")="My New Item Name"
rs.Fields("ItemPrice")=1.00
rs.Update
Note I didn't explicitly change the value of rs.fields("ItemAddedDate")...does rs.Fields("ItemAddedDate")=rs.Fields("ItemAddedDate") occur implicitly, which would force the rebuild of all the non-clustered indexes?
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Jun 25, 2015
I have a requirement to only rebuild the Clustered Indexes in the table ignoring the non clustered indexes as those are taken care of by the Clustered indexes.
In order to do that, I have taken the records based on the fragmentation %.
But unable to come up with a logic to only consider rebuilding the clustered indexes in the table.
create table #fragmentation
(
FragIndexId BigInt Identity(1,1),
--IDENTITY(int, 1, 1) AS FragIndexId,
DBNAME nvarchar(4000),
TableName nvarchar(4000),
[Code] ....
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Sep 17, 2006
What is the difference please?
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Jul 31, 2002
Sir,
1. How do I call the indexes created in SQL server for a table from Front end VB programming ?
2. How can I use SEEK command with ADODB control ?
Please give me some tips & samples
Sundar Raman
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Jul 23, 2001
Does anyone have the idea why the Indexes with _WA.....(like _WA_Sys_au_fname_07020F21) gets created.I don't how this index got created. I did not create this Index.
My Question is does the system creates these indexes or something else does this.
Thanks
Chak
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Jul 27, 2000
Is there a way to tell how many indexes exist for an entire database, all I'm looking is for a count or generating a report list.
any help would be appreciated, thank you
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Sep 13, 2000
At present I have been assigned to create indexes to retrieve the information fast, from the table. The existing table doesn’t have primary key, foreign key and unique constraints but I found to many default indexes already created by the system. I would like to know how this happened? Please inform how to delete these default indexes. Further, inform me other possible ways for the faster retrieval in SQL sever 7.0, if there are any.
I would appreciate if you send me a step by step explanations for the above problems.
Thanks a lot
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Nov 20, 2000
I have run into a snag on my development server. Queries that are selecting data based on indexed fields in a where clause are using the wrong indexes. They are arbitrarily using the clustered index which isn't in the select at all and causing big performance problems. I can run the same statements on my production server and it runs based on the proper indexes. I used query execution plans to determine that this was infact the case.
I run DBCC Checkdb everynight and it comes back with no errors. I also rebuild the indexes. We also don't receive any other errors inputting or updating data. This sounds like corruption to me but if it's something else I don't want to spend the night restoring from production if there is another reason.
Has anyone encountered this before? Any ideas?
Appreciate it, K.
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Jan 10, 2001
Is there any way for me to find out when last indexes have been used so that the one I don't need can be dropped.And also the one's that are of no use at all.
I need this as i am trying to dump all duplicated indexe . i know i can do this in ver 7
thanks
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Feb 5, 2000
when executed sp_help tablename, I get lot of statistics and indexes like the following. Can anyone please tell me how it is generated automatically. as far i know statistics are generated only for primary keys. Can you please tell me what is clustered , hypothetical and the indexes starting with _WA supposed to be. Also there are lot of duplicate stats. Is it Ok to deletes those.
_WA_Sys_is_platinum_0A9D95DB
_WA_Sys_active_0A9D95DB nonclustered, statistics, auto create located on PRIMARY Active
hind_c_33_15 nonclustered, statistics located on
hind_c_37_1 clustered, hypothetical located
Thanks
Raj
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Mar 2, 2001
Is there a way T-SQL script can find out all indexes built on a set of tables, drop them and periodically ( quarterly as an example ) re-build them ?
Thanks in advance for help.
Ivan
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Mar 5, 2001
How do you find out indexes ( with column names info ) on a table ?
Thanks in advance.
Ivan
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Jun 20, 2001
I am on SQL 6.5.
I have a question about speed and indexes. I have a static table (no updates except once a year). I want to be able to search data quickly on one column or many columns. I have created nonclustered indexes on each of the columns I search by. Is there anything else I can do to speed up my queries? Unfortunately all the searches involve using the like operator. I have even broken my table down into 2 smaller tables (Table A ~ 3 million rows, Table B 8 million rows).
All suggestions will be appreciated.
Thanks,
Eric
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Nov 12, 1998
We have to interduce a new naming convention for the indexes currently available in the user databases.
We also have to drop all the old indexes available in about 250 tables and recreate them all acording to the naming convention we are coming up with.
Can any body suggest any idea.
I thank you guys in advance for your considaration.
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Mar 10, 2006
hi.
there 2 different queries
1
[MYSQL].... where Cat=@CatID and Date=@Date[/MYSQL]
2
[MYSQL]... where Cat=@CatID and Date=@Date and Salesman=@SID[/MYSQL]
these queries are often used.
my question is about indexes.
should I use two different indexes?
index 1 : Cat,Date
index 2 : Cat,Date,Salesman
or only index 2 is enough ?
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Jul 11, 2006
I need to alphabetize PART of a union all query, and was told that this may be accomplished with an index. I tried joining two views, but it does not work! I have NO experience with indexes and need some help.
Here is my code:
Select id, country from countries where id = 6 union all Select id, country from countries where id <> 6
I want the country with id 6 (USA) to be the default on a drop down list, then all the other countries listed after it in alphabetical order. Can you do this with an index? If so, how do I proceed?
Thanks!
Ronna
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Nov 15, 2004
Hi all,
I want to know all indexes in database.
What do I do to get them?
Thanks in advanced,
Thi Nguyen
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Feb 6, 2006
We recently updated some of the databases from MS Access 2000 to SQL Server 2000. In Access we had columns which were set to Indexed No Duplicates, these were not Primary key fields. Is this possible to set some indexes to prevent duplicates in SQL Server without creating performance issues?
Miranda
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Feb 16, 2006
Do you have to take the DB offline to create or run indexes in SQL Server 2000??
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May 30, 2007
Q1
The table i have stores max 2000 records. Not sure if i neeed a clustered index for this few records. I guess not.
Q2
For the same table as above. How do you create primary keys if there is not unique records.
Do i create a new column? like newColumnID identity? and create a primary key on this new column? Ok even if i create this newcolumn. I don't think it will improve the retrieving speed cause i'm not selecting this column.
Opinions, ideas?
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Aug 24, 2007
i am running a stored procedure which has got clustered indexes created after creating table and data is inserted into it after creating clustered indexes. The tables which are meant in this sp is temporary tables and how to gain the performance of a query
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Nov 16, 2007
I've created indexes for the queries below running select getdate() before and after the query to determine the time. I'm curioius as to how sql server determines and decides how and when to use the indexes for the queries and how the run times of these queries compare. I'm also curious to know what kind of difference there would be on the last two queries as the only difference is the values.
For the last two queries I don't think there would be a difference but hoping that someone would know.
Below are my results:
select count(distinct CustomerID)
from Orders
where Status = 5
SELECT getdate()
go
Create Index Orders_Index On Orders(customerID)
go
SELECT getdate()
select sum(TotalDue)
from Orders
where CustomerID = 11212
select getdate()
go
Create Index Orders_Index On Orders(customerID)
go
select getdate()
select count(distinct AccountNumber)
from Orders
where SalesPersonID = 288
select getdate()
go
Create Index Orders_Index On Orders(salespersonID)
go
select getdate()
select count(distinct AccountNumber)
from Orders
where SalesPersonID = 276
select getdate()
go
Create Index Orders_Index On Orders(salespersonID)
go
select getdate()
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Sep 13, 2007
where can i find a example on how tobuild a script to reindex all my tablesTksDaveP
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