All of the 3 books I've read say it is not a good idea to create a clustered index on the primary key but it is created as the default. My question is has this changed in 2005? My understanding is to create the clustered index on columns used first in join clauses and then in where clauses, what is the answer?
View 14 Replieswhat the best practice is for creating indexes on columns that are foreign keys to the primary keys of other tables. For example:
[Schools] [Students]
---------------- -----------------
| SchoolId PK|<-. | StudentId PK|
| SchoolName | '--| SchoolId |
---------------- | StudentName |
-----------------
The foreign key above is as:
ALTER TABLE [Students] WITH CHECK ADD CONSTRAINT [FK_Students_Schools]
FOREIGN KEY([SchoolId]) REFERENCES [Schools] ([SchoolId])
What kind of index would ensure best performance for INSERTs/UPDATEs, so that SQL Server can most efficiently check the FK constraints? Would it be simply:
CREATE INDEX IX_Students_SchlId ON Students (SchoolId)
Or
CREATE INDEX IX_Students_SchlId ON Students (SchoolId, StudentId)
In other words, what's best practice for adding an index which best supports a Foreign Key constraint?
I have a 3rd party app which had a primary key with about 5 fields. The last field of this was a trantype. This app had a posting process which uses this in it's sql. Ran rather slow. We added an individual index to this field and cut processing down 90%. It almost seemded like sl server was ignoring this index. Is this because it was the last field in the primary key index?
View 1 Replies View RelatedI have a deal table, each of these investments must be unique. I created a int pk : idDeal. Does that make sense or should i just use the deal colm being it has a unique constraint,
Reguarding indexes, should i make the auto # colm my pk and make that the clustered index? and put another index on the Deal Colmn? Any suggestions welcomed
Thank you
I wanted to find all occurrences of ADRSCODE in a Database where ADRSCODE is in either an Index or a Primary Key.
I know how to get all of the occurences of ADRSCODE in a database and the table associated with it, I just want to tack on the Index and/or primary key.
SELECTOBJECT_NAME(object_id)FROMsys.columns
WHEREname
='foo'
How can I get the other bit of information ?
Hi everyone, I am trying to upgrade a 2000 DB to 2005 with SSIS Database Transfer.
I finally got it to work with an online transfer but the destination database has no primary keys, indexes or identity columns from the source DB.
What am I missing?
What other ways are there to upgrade a SS2000 DB to 2005?
Thank you.
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?
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] ....
Hi,
I have recently been looking at a database and wondered if anyone can tell me what the advantages are supporting a unique collumn, which can essentially be seen as the primary key, with an identity seed integer primary key.
For example:
id [unique integer auto incremented primary key - not null],
ClientCode [unique index varchar - not null],
name [varchar null],
surname [varchar null]
isn't it just better to use ClientCode as the primary key straight of because when one references the above table, it can be done easier with the ClientCode since you dont have to do a lookup on the ClientCode everytime.
Regards
Mike
Hello,
I have a table which has a composite primary key consisting of four columns, one of them being a datetime called Day.
The nice thing afaik with this composite key is that it prevents duplicate entries in the table for any given day. But the problem is probably two-fold
1. multiple columns need to be used for joins and I think this might degrade performance?
2. in client applications such as asp.net these primary keys must be sent in the query string and the query string becomes long and a little bit unmanagable.
A possible solutions I'm thinking of is dropping the existing primary key and creating a new identity column and a composite unique index on the columns from the existing composite key.
I would like to have some tips, recommendations and alternatives for what I should do in this case.
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?
View 2 Replies View RelatedWhat is the easiest way to remember the definitions of clustered and non clustered indexes.
View 9 Replies View RelatedWe 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]....
Hello again,
I'm going through my tables and rewriting them so that I can create relationship-based constraints and create foreign keys among my tables. I didn't have a problem with a few of the tables but I seem to have come across a slightly confusing hiccup.
Here's the query for my Classes table:
Code:
CREATE TABLE Classes
(
class_id
INT
IDENTITY
PRIMARY KEY
NOT NULL,
teacher_id
INT
NOT NULL,
class_title
VARCHAR(50)
NOT NULL,
class_grade
SMALLINT
NOT NULL
DEFAULT 6,
class_tardies
SMALLINT
NOT NULL
DEFAULT 0,
class_absences
SMALLINT
NOT NULL
DEFAULT 0,
CONSTRAINT Teacher_instructs_ClassFKIndex1 FOREIGN KEY (teacher_id)
REFERENCES Users (user_id)
)
This statement runs without problems and I Create the relationship with my Users table just fine, having renamed it to teacher_id. I have a 1:n relationship between users and tables AND an n:m relationship because a user can be a student or a teacher, the difference is one field, user_type, which denotes what type of user a person is. In any case, the relationship that's 1:n from users to classes is that of the teacher instructing the class. The problem exists when I run my query for the intermediary table between the class and the gradebook:
Code:
CREATE TABLE Classes_have_Grades
(
class_id
INT
PRIMARY KEY
NOT NULL,
teacher_id
INT
NOT NULL,
grade_id
INT
NOT NULL,
CONSTRAINT Grades_for_ClassesFKIndex1 FOREIGN KEY (grade_id)
REFERENCES Grades (grade_id),
CONSTRAINT Classes_have_gradesFKIndex2 FOREIGN KEY (class_id, teacher_id)
REFERENCES Classes (class_id, teacher_id)
)
Query Analyzer spits out: Quote: Originally Posted by Query Analyzer There are no primary or candidate keys in the referenced table 'Classes' that match the referencing column list in the foreign key 'Classes_have_gradesFKIndex2'. Now, I know in SQL Server 2000 you can only have one primary key. Does that mean I can have a multi-columned Primary key (which is in fact what I would like) or does that mean that just one field can be a primary key and that a table can have only the one primary key?
In addition, what is a "candidate" key? Will making the other fields "Candidate" keys solve my problem?
Thank you for your assistance.
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 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".
Pls let me know How I generate script for All primary keys and foreign keys in a table. Thereafter that can be used to add primary keys and foreign keys in another databse with same structure.
Also how I script default and other constraints of a table?
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...
View 3 Replies View RelatedHello,
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.
Thanks in Advance,
Rohit
Can somebody explain to me how to best do inserts where you have primary keys and foreign keys.l'm battling.
Is there an article on primary keys/Pk ?
hi,
how clustered indexes and non-clustered indexes been saved in memory?
non-clustered is a table of a references to the actual table?
and what about clustered indexes?
thanks.
Can anyone help ?
If you have a clustered index on an identity field are appends then forced onto the last page anyway because of the identity field order. So is there any advanbtage of having a clustered identity field ?
I need to convert several tables that currently have nonclustered indexes (primary keys) to clustered. Could anyone suggest what the easiest way of doing this would be.
View 1 Replies View Relatedhi
can someone tell me why there are only 249 non-clustered indexes,
is there any significance to that number
Hi,The more I read, the more confused I'm getting ! (no wonder they sayignorance is bliss)I just got back from the bookstore and was flipping through some SQL ServerAdministration books.One says, that to get the best query performance, youi do two things:1. Cover all the columns used in each SELECT (including the WHERE, ORDERBY , etc.) with an index2. Make sure it's a NON-CLUSTERED index.In this way, the author says, you avoid ever going directly to the basetables for data to resolve the query - i.e. it's resolved in the index.So, for example, he argues if you have:SELECT Lname,Fname, CompanyNamefrom Contactsinner join Customerson (contacts.custid = customers.custid)that you use two non-clustered indexes:1. Lname,Fname and custid from the Contacts table2. CompanyName and custid from Customers(as opposed to the standard approach of a clustered index on the PK's ofeach table)He says that clustered indexes don't speed up performance because they'rethe same as a full table scan. Should I drop clustered indexes from mylarge tables, given that there are multiple non-clustered indexes on them?Is it better to just use multiple non-clustered indexes on a heap table?Steve
View 1 Replies View Related i have some confusions with keys and indexes.. plz let me know whether the following are correct..- Every Primary Key is a Clustered Index- A Primary Key cannot exist without a Clustered Index- Every Unique Key is a Non-Clustered Index - Non-Clustered Index is the DEFAULT Index- A table can have only 1 Primary key- A table can have only 1 Clustered Index- A table can have any number of Unique Keys- A table can have any number of Non-Clustered Indexes
What is the difference please?
View 1 Replies View RelatedSQL 7 created by default a clustered index on my primary key field. I would like to drop this index and recreate it on another field, but it is not allowing me. Error message states: "An explicit DROP INDEX is not allowed... It is being used for PRIMARY KEY CONSTRAINT enforcement." Can anybody advise how I can solve this? TIA
View 1 Replies View RelatedIs any one know of a way of changing the clustered index without creating in the middle the default clustered index
we have a big table that we use to switch the clustered index
whenever we change the clustered index we cannot change it directly we have
to drop the existing than the default clustered is built
and than we can built the new one - since it is a big table the process
takes a lot of time and I wonder if we can do it directly from one cluster
index to another
What we do not is running the following SQL:
-- remove the old index
drop index Tbl.I_oldId
GO
-- now create the newId as clustered
CREATE CLUSTERED
INDEX [I_newId] ON Tbl ([newId])
ON [PRIMARY]
GO
Any Idea ?
Thanks
David
Using SQL Server 2000 ... hopefully not too dumb a question.
Is there a performance hit using Clustered Index on a table that gets a lot of deletes?
I'm creating a Transaction Log table that will get about 4,000 inserts per day. The value of some of this historical data is worthless after a while, so I delete it.
It occurs to me that this may create a lot of fragmentation. If so, is this cleaned up during weekly "Reorganize data and index pages" in the Maintenance Plan? Do I also need to select "Remove unused space from database files"?
Additional question: I though that care needed to be taken that a clustered key be a value that always increments (datestamp, identity key, etc), yet in this write-up, it shows using randomly generated key values. I'm confused. Wouldn't it have to reorganize everything with greater values to insert the new row into the appropriate spot?
http://www.sql-server-performance.com/gv_clustered_indexes.asp
Greetings all,
What's best practice for creating clustered indexes?! Should they be added to a table AFTER it has been populated or should the clustered index be created BEFORE?
Thanks for your advice in advance.
When you Upsize from Access using the wizard, unsurprisingly, a Unique index is created on the PK field, but these are all non-clustered. I presume there isn't one definitive answer to whether a index should be clustered or not, (which I understand means the table's records are held on disk contiguously), but generally, is it worth altering these all to become clustered?
Would you selectively cluster only those tables which you think would benefit most? Leave them all unclustered and look for bottle-necks?