SQL 2012 :: Included Columns In Non-clustered Index
May 8, 2014
I am trying to tune a process that is running slowly. I analyzed the process using the Database Engine Tuning Advisor, and it recommended the creation of 3 indexes, all non-clustered:
1) ColA, include ColB
2) ColA, include ColC
3) ColA, include ColD
So... I created a single non-clustered index on:
4) ColA, include ColB, ColC, ColD
That should do the same thing, right? A look at my execution plan shows that the index I created is being scanned -- 3 times. What is puzzling me, though, is that the Database Engine Tuning Advisor is still recommending I create these 3 separate indexes, even with the index (4) that I created in existence.
If it matters, ColA, ColB, ColC and ColD are all int FKs.
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Apr 24, 2007
Hi, all experts here,
Thanks a lot for your kind attention.
As I am creating the non-clustered indexes for the tables, I dont quite understand how dose it really matter to put the columns in the index key columns or put them into the included columns of the index?
I am really confused about that and I am looking forward to hearing from you and thank you very much again for your advices and help.
With best regards,
Yours sincerely,
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Nov 14, 2011
I would like to know the impacts (if any) of adding nonclustered index with included columns on large tables (these tables are populated by bulk insert from text files).
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Mar 28, 2014
I have a table with clustered index on that. I have only 5 columns in that table. Execution plan is showing that Index scan occurred. What are the cause of the Index scan how can we change that to index seek?
I am giving that kind of similar query below
SELECT @ProductID= ProductID FROM Product WITH (NOLOCK) WHERE SalesID= '@salesId' and Product = 'Clothes '
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Oct 4, 2007
I'm using sys.dm_db_missing_index_details to find missing indexes on a database that is currently in testing. After running a bunch of our reports, there are several suggested indexes on 3 or 4 columns that have 15 - 20 included columns. The included columns are mostly varchars ranging from 1 to 150 characters along with a couple of date columns. My index size on that table is already nearly twice the size of the data.
I don't think it's a good idea to add an index with that many columns, but the information I've read on included columns is very general. I'm wondering if there is something about them that I don't understand that would make this a good idea.
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Nov 1, 2007
I have a table<table1> with 804668 records primary on table1(col1,col2,col3,col4)
Have created non-clustered index on <table1>(col2,col3,col4),to solve a performance issue.(which is a join involving another table with 1.2 million records).Seems to be working great.
I want to know whether this will slow down,insert and update on the <table1>?
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Mar 5, 2015
I have a clustered index that consists of 3 int columns in this order: DateKey, LocationKey, ItemKey (there are many other columns in this data warehouse table such as quantities, prices, etc.).
Now I want to add a non-clustered index on just one of the other columns, say LocationKey, like this:
CREATE INDEX IX_test on TableName (LocationKey)
I understand that the clustered index keys will also be added as key columns to any NC indexes. So, in this case the NC index will also get the other two columns from the clustered index added as key columns. But, in what order will they be added?
Will the resulting index keys on this new NC index effectively be:
LocationKey, DateKey, ItemKey
OR
LocationKey, ItemKey, DateKey
Do the clustering keys get added to a NC index in the same order as they are defined in the clustered index?
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Nov 14, 2006
the query:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WHERE a.AssociationGuid IN (
SELECT ada.DataAssociationGuid FROM AssociationDataAssociation ada
WHERE ada.AssociationGuid = '568B40AD-5133-4237-9F3C-F8EA9D472662')
takes 30-60 seconds to run on my machine, due to a clustered index scan on our an index on asset [about half a million rows]. For this particular association less than 50 rows are returned.
expanding the inner select into a list of guids the query runs instantly:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WHERE a.AssociationGuid IN (
'0F9C1654-9FAC-45FC-9997-5EBDAD21A4B4',
'52C616C0-C4C5-45F4-B691-7FA83462CA34',
'C95A6669-D6D1-460A-BC2F-C0F6756A234D')
It runs instantly because of doing a clustered index seek [on the same index as the previous query] instead of a scan. The index in question IX_Asset_AssociationGuid is a nonclustered index on Asset.AssociationGuid.
The tables involved:
Asset, represents an asset. Primary key is AssetGuid, there is an index/FK on Asset.AssociationGuid. The asset table has 28 columns or so...
Association, kind of like a place, associations exist in a tree where one association can contain any number of child associations. Each association has a ParentAssociationGuid pointing to its parent. Only leaf associations contain assets.
AssociationDataAssociation, a table consisting of two columns, AssociationGuid, DataAssociationGuid. This is a table used to quickly find leaf associations [DataAssociationGuid] beneath a particular association [AssociationGuid]. In the above case the inner select () returns 3 rows.
I'd include .sqlplan files or screenshots, but I don't see a way to attach them.
I understand I can specify to use the index manually [and this also runs instantly], but for such a simple query it is peculiar it is necesscary. This is the query with the index specified manually:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WITH (INDEX (IX_Asset_AssociationGuid)) WHERE
a.AssociationGuid IN (
SELECT ada.DataAssociationGuid FROM AssociationDataAssociation ada
WHERE ada.AssociationGuid = '568B40AD-5133-4237-9F3C-F8EA9D472662')
To repeat/clarify my question, why might this not be doing a clustered index seek with the first query?
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Mar 28, 2014
I want to know more details about the Clustered Index Delete. Is that Clustered Index Delete in the execution plan is good or bad or we can neglect that cost. Is there any way to avoid that clustered Index delete operator from the execution plan.
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Jul 29, 2014
- What are your thoughts on adding clustered index on datetime (createdDate , native GUID) column. The data will be be physically organized in the clustered index allowing range operations to perform its duties. But will the GUID column make any impact ( drawbacks) should it be made part of the clustered key ?
The GUID column will provide the lookup with the required indexes to support.
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Mar 16, 2015
I created a NC index as suggested by missing index DMV(of course I don't create them blindly). This one seemed to be a useful index but I now see from index usage stats that it only got scanned 50 times in 4 days.No seeks, no lookups. So is it a good idea keeping such index.The table on which this index is created is used more for reads and less for writes.
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Apr 16, 2015
Is it always the best practice to have the partition column also as the column for clustered index?
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Sep 7, 2014
how to reduce the cost of clustered index insert ?
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Dec 1, 2014
I have a query which is primarily a victim of blocking and a blocker itself for other queries. I studied the plan for this and it shows a 42% cost on CI insert operation. The insert is happening on a table (Table A) that has a PK. This PK is not a running number. It is also a business key (primary key) in another master table (Table B).
My understanding is that the cost is heavy because -
1, this PK is not an incremental number. It could be any number not in a sequence.
2. while inserting into CI, there must be a scan happening to find out the location where the index will be inserted.
How can I reduce the cost?
1. Should I go for partitioning of this table Table A? I am trying to do this but I am not able to find any suitable partition key looking at the JOINS and filter clauses where this table is being used in the applicaiton.
2. Should I introduce a surrogate key (running number) as a primary key so that CI is faster ?
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Jan 23, 2015
I have a table that has a clustered index that is only the identity column on the table. The table is somewhere around 200K rows and has 3800 pages in the index. We run our index maintenance every other day on this database using Ola's scripts and this index is rebuilt because it is 40-60% fragmented after 2 days. Overall, this isn't really too much of a problem since the index rebuild doesn't take too long, but I am puzzled as to how this index is getting fragmented since the only column in it is the identity.
CREATE TABLE [dbo].[Example](
[ExampleID] [int] IDENTITY(1,1) NOT NULL,
[ExampleCode] [varchar](10) NOT NULL,
[ForeignID] [int] NOT NULL,
[AnotherID] [int] NOT NULL,
[code]...
) ON [PRIMARY]There is nothing strange like updates to the identity happening and while some records are deleted, there has only been about 20,000 in the life of the table (months). Not enough to account for the level of fragmentation that we're seeing on the index.About the only thing I can think of that would cause fragmentation on this index in this scenario are:
1. Page splits caused by starting with a small value in one of the VARCHARs and later inserting a larger value
2. Page splits caused by the NULLABLE column, ExampleDate, starting with NULLs and later updating them to a date.
For #1, I had development check the update scenarios for the varchar columns, especially the varchar(1000) one, and they didn't see it as a common thing where the values would go from small (or empty) to large.
For #2, I checked and found that the only value for that column in the table is NULL so while it always starts as NULL, it never gets updated to anything else.
I've tried looking at sys.dm_db_index_operational_stats and the leaf_update_count is around 300,000, but unless those updates are causing page splits, I don't see how they would contribute to fragmentation.
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Apr 15, 2015
I have a clustered index which shows as having a fragmentation level of 66% according to sys.dm_db_index_ physical_ stats.avg_ fragmentation_ in_ percent.
But no matter what I try the fragmentation level doesn't budge. And yes I'm updating the statistics after each attempt.Its not a huge issue the table only has 348 records. I'm testing a fixing fragmentation maintenance script. In Ironing out the syntax of my script I've fixed the fragmentation of indexes of over 65 % anyway..I've come across and index that I can't defragment. I've tried
ALTER INDEX ALL ON [GRIDINFO] REBUILD WITH (FILLFACTOR = 90)
I've tried
ALTER INDEX ALL ON [GRIDINFO] REORGANIZE
I've tried
DBCC INDEXDEFRAG (MYDATABASE, 'GRIDINFO', PK__GRIDINFO__3214EC2721F5FC7F);
The command complete successfully yet the avg_fragmentation_in_percent doesn't change. The table also has a nonclustered index. I've gleaned through all the statements of 'this will have no effect if' but so far I've not spotted a reason why this index won't defrag.The script has been modified to remove schema and database names for the forum.
dbcc showcontig('GRIDINFO','IDX_GRIDINFO1') with tableresults , all_levels
go
DBCC SHOWCONTIG ('GRIDINFO')
go
sp_helpindex 'GRIDINFO'
[code]....
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May 7, 2014
I need to create a Clustered Index (CI) on a very large SQL Server 2012 database table. This table has about approximately 10 billion rows, 500 GB in size. The job ran for about 20 hours into it and then fails with error: "Out of disk space in tempdb". My tempDB size is 1.8TB, but yet it's still not enough.
Here is my script:
CREATE CLUSTERED INDEX CI_IndexName
ON TableName(Column1,Column2)
WITH (MAXDOP= 4, ONLINE=ON, SORT_IN_TEMPDB = ON, DATA_COMPRESSION=PAGE)
ON sh_WeekDT(Day_DT)
GO
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Nov 21, 2014
I have Enterprise version of SQL Server 2012 & SQL server 2008. I understand that Image/Text/NText is obsoleted and should not be used. That being said I dont understand why I couldnt rebuild the following clustered index, while I could with nonclustered index, this happens on both SQL 2008 and 2012. Here are the DDL.
CREATE TABLE [dbo].[Demo](
[ID] [int] NOT NULL,
[FK_ID] [uniqueidentifier] NOT NULL,
[SomeColumn] [nvarchar](100) NOT NULL,
[Image] [image] NULL
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
[code]...
An online operation cannot be performed for index 'IX1_Demo' because the index contains column 'Image' of data type text, ntext, image or FILESTREAM. For a non-clustered index, the column could be an include column of the index. For a clustered index, the column could be any column of the table. If DROP_EXISTING is used, the column could be part of a new or old index. The operation must be performed offline.
--Online rebuild works fine on non clustered index
ALTER INDEX IX2_Demo ON Demo REBUILD WITH(ONLINE = ON)--It seems to me that some how having the Image datatype column in the table is an issue. eventhough that column is not part of the index.
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Aug 8, 2015
I have a view that joins a dozen tables with a million rows added per year by an application. I want to materialize it. The view is always filtered by date first on reports, then there are a few key transaction keys, but then many other fields required to make each row unique. I don't want to add these columns since they are large, many, not used for sorting or filtering, and may not define uniqueness in a future application design. I need a uniqueifier that is application agnostic. I prefer a bigint. So to store the materialized view ideally for reporting, I want to add the following clustered index to materialize the view:
CREATE unique CLUSTERED INDEX idx1
ON [dbo].[myview](myDate, key1, key2, key3, id bigint identity(1,1) NOT NULL)
And I get this error:
Msg 102, Level 15, State 1, Line 3
Incorrect syntax near 'bigint'.
Can I do what I want? If so, how?
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Jun 3, 2014
I was under impression that rebuilding index online largely means that the index will remain available for use during rebuild and my procs and query will be able to use it during rebuild. Also my understanding was that table will be locked very briefly while the schema change will be completing.But when I was rebuilding the clustered index online on a large table with some 3 million records, the table got locked and I was not able even to read the data from it for some 5 minutes. Then I cancelled the operation as it was production server and it was one of our main transaction table.
Is rebuilding index online supposed to work this way? The table has no other index.The parameteres I used are:
REBUILD WITH (PAD_INDEX = ON, SORT_IN_TEMPDB = ON, ONLINE = ON, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 95)
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Jun 18, 2015
I have created NONCLUSTERED index on table but my report is taking more time that's why i created columnstore NONCLUSTERED index on the same table but i have one query, if any table have row and column level index(same columns in index) . Which index query will consider.
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Jul 9, 2014
I understand that minimal logging can occur on a non clustered indexed heap as long as [URL] ...
*not replicated
*tablock is used
*table is empty
The following test seems to contradict this
In the test I create a non indexed heap, insert some record and check the log, then repeat the test on an indexed heap.
The results suggest that even though the conditions for minimal logging into a indexed heap are met, minimal logging is not happening although it does happen on an non indexed heap. What am I doing wrong?
CREATE DATABASE logtest
GO
USE logtest
GO
CREATE TABLE test (field varchar(100))
GO
CHECKPOINT
[Code] ....
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Sep 4, 2015
We are going to use SQL Sever change tracking. The problem is that some of our tables, which are to be tracked, have no primary keys. There are only unique clustered indexes. The question is what is the best way to turn on change tracking for these tables in our circumstances.
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Aug 28, 2015
I desire to have a clustered index on a column other than the Primary Key. I have a few junction tables that I may want to alter, create table, or ...
I have practiced with an example table that is not really a junction table. It is just a table I decided to use for practice. When I execute the script, it seems to do everything I expect. For instance, there are not any constraints but there are indexes. The PK is the correct column.
CREATE TABLE [dbo].[tblNotificationMgr](
[NotificationMgrKey] [int] IDENTITY(1,1) NOT NULL,
[ContactKey] [int] NOT NULL,
[EventTypeEnum] [tinyint] NOT NULL,
[code]....
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Jul 19, 2013
I have created two tables. table one has the following fields,
Id -> unique clustered index.
table two has the following fields,
Tid -> unique clustered index
Id -> foreign key of table one(id).
Now I have created primary key for the table one column 'id'. It's created as "nonclustered, unique, primary key located on PRIMARY". Primary key create clustered index default. since unique clustered index existed in table one, it has created "Nonclustered primary key".
My Question is, What is the difference between "clustered, unique, primary key" and "nonclustered, unique, primary key"? Is there any performance impact between these?
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Jan 4, 2008
I have large table with 10million records. I would like to create clustered or non-clustered index.
What is the quick way to create? I have tried once and it took more than 10 min.
please help.
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Sep 8, 2006
Hi there, I have a table that has an IDENTITY column and it is the PK of this table. By default SQL Server creates a unique clustered index on the PK, but this isn't what I wanted. I want to make a regular unique index on the column so I can make a clustered index on a different column.
If I try to uncheck the Clustered index option in EM I get a dialog that says "Cannot convert a clustered index to a nonclustered index using the DROP_EXISTING option.". If I simply try to delete the index I get the following "An explicit DROP INDEX is not allowed on index 'index name'. It is being used for PRIMARY KEY constraint enforcement.
So do I have to drop the PK constraint now? How does that affect all the tables that have FK relationships to this table?
Thanks
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Mar 31, 2014
When creating a column store index, are there any reasons not to include all columns, besides index size of course? i.e. will the index be more versatile with more columns or should I treat it exactly like its a standard index, putting only necessary columns, in the correct order?
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Oct 15, 2007
Hi everybody!
I just ran the Database Engine Tuning Advisor on a relative complex query to find out if a new index might help, and in fact it found a combination that should give a performance gain of 94%. Fair enough to try that.
What I wonder about: The index I should create contains 4 columns, the last of them being the Primary Key column of the table, which is also my clustered index for the table. It is an identity integer btw.
I think I remember that ANY index does include the clustered one as lookup into the data, so having it listed to the list of columns will not help. It might at worst add another duplicate 4 bytes to each index entry.
Right? Wrong? Keep the column in the index, or remove it since it is included implicit anyway?
Thanks for suggestions!
Ralf
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Jul 28, 2015
I used following query to identify missing indexes:
SELECT mid.statement , mid.included_columns, mid.equality_columns, mid.inequality_columns,
migs.avg_total_user_cost * (migs.avg_user_impact / 100.0) * (migs.user_seeks + migs.user_scans) AS improvement_measure,
'CREATE INDEX [NCIX_' + CONVERT (varchar, mig.index_group_handle) + '_' + CONVERT (varchar, mid.index_handle)
+ '_' + LEFT (PARSENAME(mid.statement, 1), 32) + ']'
+ ' ON ' + mid.statement
[Code] ....
I think I need to only create few if an index is covering all columns then I do not need to create more indexes for separate columns or should I create separate index as suggested?
Similarly:
CREATE INDEX [NCIX_20187_20186_TL_SRV_Stationary_Stock_Transact] ON [TL_SRV_Stationary_Stock_Transaction] ([SerialNo],[StationaryStatus]) GO
CREATE INDEX [NCIX_20189_20188_TL_SRV_Stationary_Stock_Transact] ON [TL_SRV_Stationary_Stock_Transaction] ([StationaryStatus]) INCLUDE ([SerialNo]) GO
[Code] ....
Should I create all indexes above or use minimum number of indexes which covers all columns as mentioned in above create index statements?
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Dec 5, 2007
Dear All.
We had Teradata 4700 SMP. We have moved data from TD to MS_SQL SERVER 2003. records are 19.65 Millions.
table is >> Order_Dtl
Columns are:-
Client_ID varchar 10
Order_ID varchar 50
Order_Sub_ID decimal
.....
...
..
.
Pk is (ClientID+OrderId+OrderSubID)
Web Base application or PDA devices use to initiate the order from all over the country. The issue is this table is not Partioned but good HP with 30 GB RAM is installed. this is main table that receive 18,0000 hits or more. All brokers and users are using this table to see the status of their order.
The always search by OrderID, or ClientID or order_SubNo, or enter any two like (Client_ID+Order_Sub_ID) or any combination.
Query takes to much time when ever server receive more querys. some orther indexes are also created on the same table like (OrderDate, OrdCreate Date and Status)
My Question are:-
Q1. IF Person "A" query to DB on Client_ID, then what Index will use ? (If any one do Query on any two combination like Client_ID+Order_ID, So what index will be uesd.? How does MS-SQL SERVER deal with these kind of issues.?
Q2. If i create 3 more indexes on ClientID, ORderID and OrdersubID. will this improve the performance of query.if person "A" search record on orderNo so what index will be used. (Mind it their would be 3 seprate indexes for Each PK columns) and composite-Clustered index is also available.?
Q3. I want to check what indexes has been used? on what search?
Q4. How can i check what table was populated when, or last date of update (DML)?
My Limitation is i Dont Create a Partioned table. I dont have permission to do it.
In Teradata we had more than 4 tb record of CRM data with no issue. i am not new baby in db line but not expert in sql server 2003.
I am thank u to all who read or reply.
Arshad
Manager Database
Esoulconsultancy.com
(Teradata Master)
10g OCP
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Jul 3, 2006
Hi everyone,
When we create a clustered index firstly, and then is it advantageous to create another index which is nonclustered ??
In my opinion, yes it is. Because, since we use clustered index first, our rows are sorted and so while using nonclustered index on this data file, finding adress of the record on this sorted data is really easier than finding adress of the record on unsorted data, is not it ??
Thanks
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Jun 2, 2014
Usually it is better to include the columns in the index that are in where clause, select list and join.I am thinking that the columns in the selected list is better to keep as index columns and the columns that are in the where clause is better to keep in key columns.Where do we use join column is it better to create as main key column or included column.
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