Would it be OK to use varchar(5) instead of char(5) as the first field of a
composite clustered index?
My gut tells me that varchar would be a bad idea, but I am not finding much
information on this topic on this when I Google it.
Currently the field is Char(4), and there is a need to increase it to hold 5
characters.
TIA
When we create a composite key(col1,col2) clustered index is created in both col1 and col2.So how come "only one clustered can be created for a table" is justified?
View 8 Replies View RelatedIs that possible on SQL Server 2000 and onwards?
View 1 Replies View RelatedWant to check my thinking with you folks...
I have a table with a clustered composite index, consisting of 3 columns, which together form a unique key. For illustration, the columns are C1, C2 & C3.
Counts of distinct values for columns are C1 425, C2 300,000 & C3 4,000,000
C3 is effectively number of seconds since 01/01/1970.
The usage of the table is typically, insert a row, do something else, then update it.
Currently, the index columns are ordered C3,C1,C2. Fill factor of 90%.
My thinking is that this composite index is better ordered C1,C2,C3.
My reasoning is that having C3 as the leading column, biases all the inserts towards one side of the indexes underlying B-tree, causing page splits. Also, there'll be a bunch of "wasted" space across the tree, as the values going into C3 only ever get bigger (like an identity), so the space due to the fill factor in lower values never gets used.
Welcome your thoughts.
I created composite clustered index key based on Gender and Salary column
The Query executed Successfully and <g class="gr_ gr_135 gr-alert gr_tiny gr_spell undefined ContextualSpelling multiReplace" data-gr-id="135" id="135">i</g>
got composite index key id Gender(-), Salary I <g class="gr_ gr_310 gr-alert gr_gramm undefined Grammar only-ins replaceWithoutSep" data-gr-id="310" id="310">want</g> know why Gender(-) display like this?
And Gender is <g class="gr_ gr_391 gr-alert gr_spell undefined ContextualSpelling ins-del multiReplace" data-gr-id="391" id="391">nvarchar</g> (20)
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
One table I manage has a clustered index, and it includes somevarchar columns. When it is initially created, all the columnsin the clustered index are populated, and then some of the longervarchars are populated through update queries. If the varcharcolumns are stored outside the clustered structure, then it wouldmake sense to create the clustered index before populating thevarchar columns. Otherwise it would make sense to wait, becausepopulating the varchars might cause page splits. Are varcharcolumns stored on the page along with the fixed-size columns, orare they managed separately with the page containing pointersto them?Thanks,Jim Geissman
View 5 Replies View RelatedHi,
What is the difference updating a null value to char/varchar type column
versus empty string to char/varchar type column?Which is the best to do and why?
Could anyone explain about this?
Example:
Table 1 : tCountry - Name varchar(80) nullable
Table 2 :tState - Name char(2) nullable
Table 3 :tCountryDetails - countryid,state (char(2) nullable) - May the country contain state or no state
So,when the state is not present for the country ,i have two options may be - null,''
tCountryDetails.State = '' or tCountryDetails.State = null?
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?
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.
View 4 Replies View RelatedI 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]....
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?
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.
I have a table that contains a lot of demographic information. The data is usually small (<20 chars) but ocassionally needs to handle large values (250 chars). Right now its set up for varchar(max) and I don't think I want to do this.
How does varchar(max) store info differently from varchar(250)? Either way doesn't it have to hold the container information? So the word "Crackers" have 8 characters to it and information sayings its 8 characters long in both cases. This meaning its taking up same amount of space?
Also my concern will be running queries off of it, does a varchar(max) choke up queries because the fields cannot be properly analyzed? Is varchar(250) any better?
Should I just go with char(250) and watch my db size explode?
Usually the data that is 250 characters contain a lot of blank space that is removed using a SPROC so its not usually 250 characters for long.
Any insight to this would be appreciated.
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
Hi folks, i need an advise.
I've a gerand table customers_orders table with customer_id and order_id.
Whenever we have to find orders, for customer, this table is involved. Hey; i know u'll be angry y the heck this gerand exist but i've to blame the older dudes then.
Now this table has composite clustered index; CUSTOMER_ID+ORDER_ID.
The tables have grown over GB size; i see HASH INNER JOIN rather than MERGE for the GEREND and CUSTOMER table join.
Is it good to use composite clustered index; or should i clustered one the columns in the GEREND and other to normal index. What performance impact it could be.
Howdy!
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
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 ?
Thanks
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>?
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
How do I improve a 3 column, composite clustered index on a large table when the developer insists there is no other way to achieve uniqueness? They say a uniqueindentifier column will not work.
View 5 Replies View RelatedHi,I created a composite index (lastname, firstname). I know the followingqueries will use this index:WHERE lastname = ...WHERE lastname = ... AND firstname = ...Also this won't use the index:WHERE firstname = ...But how about: WHERE firstname = .. AND lastname = ...And why?Thanks a lot,Baihao--Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
View 13 Replies View RelatedI 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?
Quick question about the primary purpose of Full Text Index vs. Clustered Index.
The Full Text Index has the purpose of being accessible outside of the database so users can query the tables and columns it needs while being linked to other databases and tables within the SQL Server instance.
Is the Full Text Index similar to the global variable in programming where the scope lies outside of the tables and database itself?
I understand the clustered index is created for each table and most likely accessed within the user schema who have access to the database.
Is this correct?
I am kind of confused on why you would use full text index as opposed to clustered index.
Thank you
Goldmember
Hi,
Does any body know of any performance implications of using 'varchar' data type against 'char'?
I have some columns that are using 'char' data type, but the data in them is not fixed length. So, to gain some disk space I am planning to change the data type to 'varchar'. But, I am concerned if there will be any performance de-gradation or any other implications of doing this.
Regards
Chakri
Hi,
Is that true that using CHAR datatype improves the performance comparing to VARCHAR
thanks
indeed.
Why would you want to use char when you have varchar? Is there any performance hit using a varchar and the size you make that varchar?
Debate going at work.
Phil
I have recently inherited a database where all of the tables use varchar instead of chars for fields. Very , very few of these fields are involved in keys of even indices, but performance is an issue. I thought that I had read that varchars are worse for performance than chars when page splits may occur. Is this related to updates only, or does it matter?
Any help appreciated.
In relation to the code in this thread
http://forums.databasejournal.com/showthread.php?t=42622
My customer code field is Char (8) but accept an argument of Varchar (8) to my stored procedure. Don't ask me why!?!!
The customer code could be anything from 'A' to 'ZZZZZZZZ'.
Will this have any effect especially relating to overhead and retrieving incorrect data?
Hi,
This question may sound silly,but please comment.
Please tell me a situation where char should be used and not varchar.
Let us assume that we are dealing with non unicode characters.
Well, I find varchar is always smarter than char, so why char?
Thanks!!
Rudra
i would like to know if there is an overhead in using VARCHAR when you use to store it...
a colleague of mine claims that if the field is defined to be VARCHAR the system creates and additional column DOUBLE/DECIMAL with storage size of 17/18bytes.
such that if the size of the varchar field is less than 30 it is better to be defined as CHAR instead.
please help me out here... i think there's something wrong with his statement, but i need concrete proof to it... a link to page or pdf file would be very much appreciated.
Greetings,I have a question. I work on some SQL2k/ASP.NET apps at work. Mypredacessor, who created the databases/tables seemed to have liked touse 'char' for all text fields. Is there a reason why he would havedone this over using varchar? It's a minor annoyance to always have toRTRIM data and it makes directly making changes to the database moreannoying (with all the pointless trailing spaces)?I usually use char for fixed string lengths, like state abbreviationsor something, and varchar for strings of unknown length.Is it a performance issue? Our database doesn't do much traffic, forthe most part.
View 5 Replies View RelatedHi ,Have a Visual C++ app that use odbc to access sql server database.Doing a select to get value of binary field and bind a char to thatfield as follows , field in database in binary(16)char lpResourceID[32+1];rc = SQLBindCol(hstmt, 1, SQL_C_CHAR,&lpResourceID,RESOURCE_ID_LEN_PLUS_NULL , &nLen1);and this works fine , however trying to move codebase to UNICODE antested the followingWCHAR lpResourceID[32+1];rc = SQLBindCol(hstmt, 1, SQL_W_CHAR,&lpResourceID,RESOURCE_ID_LEN_PLUS_NULL , &nLen1);but only returns 1/2 the data .Any ideas , thoughts this would work fine , nit sure why loosing dataAll ideas welcome.JOhn
View 2 Replies View Related