Table has a 4 part primary key. All BigInt data types. Key value 1 and 2 have a range between 1 and 100. Key values 3 and 4 are auto incrementing values (forign key values) from other tables.
Space is an issue, so we have chosen not to have an additional column for a counter field for the PK. (We would never use the field for querying.)
Users complained of query speeds, so we added a couple non clustered indexs. This brought up the query speeds a lot. But of course it slowed down the input speed a bit. Nothing dramatic, but enough so we could tell.
Now the users was to increase the amount of data by about 5X. Obviosly I'm somewhat concerend, as SQL is already spending a lot of the day pegged.
So, in looking around, since the new indexes seem to be the most help in querying, I'm thinking of dropping the PK back to a nonclustered index, so I can get rid of the over head of restructring the data table on every insert. Then maybe making one of the other indexes the clustered index. (only 2 columns in this index)
Table A (15 field, 4 fields indexed and Primary Key) – approximate rows: 50.000 – 60.000
Table B (18 field, 6 fields indexed and Primary Key) – approximate rows: 350.000 – 500.000
Table C (16 filed, 9 fields indexed and Primary Key) – approximate rows: 500.000 – 1.000.000
Structure is something like this: A (master) --> B (detail) ---> C (sub detail)
On each 3 table is added new record, in table C the record is added after a search in table B. My question is: Which is the best method? CLUSTERED INDEX or NONCLUSTERED INDEX
i only know you use clustered when you have million of records. So once the table has been indexed, query statement is able to retrieve the recordset faster.
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 ??
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.
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,
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?
Hi You know when you reread something you've read many times and a penny suddenly seems to drop and you realise that you probably just never quite got it afterall? If creating a nonclustered index with no includes statement it is totally pointless to specificy a fillfactor other than 0 or 100 if you do not also use the PAD_INDEX option? Thought I'd make it a poll just for the hell of it.:)
Hi guys. I have a table named [Check] and need to create an index for CVNumber field. The table has no primary key for the meantime. I tried this script but error occured.
BEGIN TRANSACTION SET QUOTED_IDENTIFIER ON GO SET TRANSACTION ISOLATION LEVEL SERIALIZABLE GO COMMIT BEGIN TRANSACTION CREATE NONCLUSTERED INDEX IX_Check_1 ON dbo.[Check] ( CVNumber ) ON [PRIMARY] GO COMMIT
Error message:
Server: Msg 3023, Level 16, State 2, Line 3 Backup, CHECKALLOC, bulk copy, SELECT INTO, and file manipulation (such as CREATE FILE) operations on a database must be serialized. Reissue the statement after the current backup, CHECKALLOC, or file manipulation operation is completed. Server: Msg 3902, Level 16, State 1, Line 1 The COMMIT TRANSACTION request has no corresponding BEGIN TRANSACTION.
Is it because I used the table name Check which is a reserved word for SQL? But I included [ ].
Hi everyone, I have some problems on composite nonclustered indexes. I could not exatly understand their logic. In my opininon, suppose that we have a table called Order and we create a composite nonclustered index on this table for OrderID column and OrderDate column. So I am using this query;
SELECT * FROM Order WHERE OrderID > 12 ORDER BY OrderDate So in here, I think our first research is based on OrderID and ten after ordering our data pointer according to the OrderID and then our index is converted to an index which is based on OrderDate while performing ordering. So is this correct ?? Would you please explain this ?
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?
I have a really super slow stored proc that does something simple. it updates a table if certain values are received.
In looking at this the matching is done on the Primary Key, which is set as a Clustered index, looking further I have another constraint, that sets the same column to a Unique, Non-Clustered.
I am not sure why this was done, but it seems to be counter productive. I have read only references to Which one is better on a primary key, but not can their be both and if it is "Smart".
A few days after droping and recreating noclustered indexes on a large table, scan density of most indexes falls below 20%. Only a few number of rows has deleted. Update operation didn't update these keys and there was a lot of inserts. Could anyone explain why are indexes fragmented so much?
When a nonunique nonclustered index is built on top of a clusteredindex, is it guaranteed that the bookmark in the nonclustered indexwill be kept in the same order as the clustered index?Here's an example to demonstrate my question:CREATE TABLE indextest (col1 int NOT NULL,col2 int NOT NULL,col3int,col4 int)ALTER TABLE indextest ADD PRIMARY KEY CLUSTERED (col1,col2)CREATE INDEX ix_indextest ON indextest (col1,col3)GOINSERT indextest VALUES (1,2,1,1)INSERT indextest VALUES (1,3,2,1)INSERT indextest VALUES (1,4,2,1)INSERT indextest VALUES (2,1,1,1)INSERT indextest VALUES (1,1,1,1)SELECT col1,col2 FROM indextest WHERE col1=1 AND col3=1DROP TABLE indextestThe select statement above is covered by the nonclustered index, sothat index is used. However, the nonclustered index is defined only toensure the ordering of col1 and col3 within the index; col1 and col2follow within the index as the bookmark to the clustered index. When Irun this query, my desired result is to have the records appear in theorder supported by the clustered index:1,11,2As it happens, the result I got was indeed in that order, but I don'tknow if it was mere coincidence, or if the bookmark in the nonclusteredindex is maintained in the same order as the clustered index. If Iwant to ensure the above order, is it sufficient to have thenonclustered index defined as above, or do I need to define it as:create index ix_indextest on indextest (col1,col3,col2)just to be sure that the results are returned in ascending order forcol1,col2? If the two-column index is sufficient, is it guaranteed tostill be sufficient in SQL2005 and future versions of SQL Server, or amI better off adding the third column just to be safe?Thank you,--Dennis Culley
I have table which having clustered index based on column (A,B,C,D,E,F).Now my query based on B,D,F. e.g: where b='Test1' and D='test2' and F='test3' Now Execution plan ask to create non clustered index with (B,D,F) column.is it make any sense to create non clustered index where clustered already available.
I've a table with primary key defined as non-clusterd, now without dropping it can I modify the existing index to clustered through tsql as I had to write some migration script and in that script I wanna do this.
I have a scenario where I have 3 columns and all 3 of them are used in the where clauses of simple queries or ones having joins .
TABLE( Column1 int FLAG1 bit FLAG2 bit )
Sample queries :
Select * from TABLE where FLAG1 =1 and FLAG2 =0 (Any combination of these flags) Select * from TABLE inner join SOMEOTHERTABLE on TABLE.Column1 = SOMEOTHERTABLE .Column1 where FLAG1 =1 and FLAG2 =0
( any join and combination of flags)
Questions :
What would be the best nonclustered index strategy :
Column1 as the index key including FLAG1 and FLAG2 or Column1,FLAG1 and FLAG2 in the index key
Points to note :
The queries are part of an ETL process and are used to track new records vs old records. The Flags switch states within the same job . So if we are creating an index on all 3 columns, the index has to be reorganized more than once based on the flag states. If we keep them in the include list , then its only about updating the leaf data with the latest flag values.
On the other hand, an index on all 3 columns will result in an index Seek alone , where as for the included list , there will be an index seek and a predicate .
Does the predicate cause more overhead than reorganizing the index or is it the opposite ?
I would like to find information on Clustered and Non-clustered indexes and how B-trees are used. I know a clustered index is placed into a b-tree which makes sense for fast ordered searching. What data structure does a non-clustered index use and how? I tried to find info. on the web but couldn't get much detail...
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>?
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?
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?
We have a table, which has one clustered index and one non clustered index(primary key). I want to drop the existing clustered index and make the primary key as clustered. Is there any easy way to do that. Will Drop_Existing support on this matter?
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.
Dear All, i've observed one particular table, one column is having clustered and non clustered index. is it ok? or i need to drop the non clustered column?
the table has 16 columns and at present 8 million records are there. per day approxmately 60000 rows will be getting into the table. it has another 3 non clustered indexes.
please suggest me.
Arnav Even you learn 1%, Learn it with 100% confidence.
