Keys And Indexes
May 26, 2008
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
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Jul 16, 2014
what 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?
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Oct 29, 2005
Hello,
I am new in SQL Server, I have to deal with this big database with many tables, is there any way I can get a list of all primary keys , foreign keys and indexes and on all tables?
Thanks,
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May 6, 2005
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?
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Jul 20, 2005
I'm trying to drop all indexes and primary keys so that i can rebuild them(from a script created from same database on another server).when i go to the 'generate sql scripts', it has the ability to drop orgenerate alltables. it also has the ability to generate all keys only. but i cant finda wayto drop all of these keys...any ideas?tiawoody rao
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May 19, 2004
is there a function that i can use in a store procedure that allow me to create an Indexes/Keys Property
thanx
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Aug 18, 2006
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?
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Jan 25, 2006
I 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
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Sep 21, 2007
If i create a simple table with a foreign key constraint, does itcreate an implicit index on that given ID? I've been told this isdone in some databases, but i need to know for sure if SQL Server doesit. Has anyone heard of this before, on any other databses perhaps?Heres an example of how the foreign key constraint is being added:ALTER TABLE [dbo].[administrators] WITH CHECK ADD CONSTRAINT[FPSLUFSUOXZGAJOJ] FOREIGN KEY([AdministratorRoleID])REFERENCES [dbo].[administratorroles] ([AdministratorRoleID])My initial testing seems to indicate adding an index on the foreignkey column helps, but i need to know for sure. Any insight would begreatly appreciated!Bob
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Oct 12, 2015
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 ?
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Mar 25, 2008
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.
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Feb 20, 2007
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.
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Apr 11, 2006
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.
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May 16, 2008
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?
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Jul 15, 2002
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 ?
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Nov 22, 2007
Hello!I have a table A with fields id,startdate and other fields. id and startdateare in the primary key.In the table B I want to introduce a Foreign key to field id of table A.Is this possible? If yes, which kind of key I have to build in table A?Thx in advance,Fritz
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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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Aug 13, 2007
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
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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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May 24, 2004
hi
lets say i have table student(id,name) id =pk
table course(cno,cname)cn=pk
now iam a fresh graduate as i learned from uni if i want to get the couses that each student took i would make a table called studentcouse(id,cno) and put the two of them pk
now iam working and at work they told me to do so:studentcouse(studentcouse_serial,id,cno) studentcouse_serial=pk .but i told them that dublicate filed may occur amd they told me that we have a function that will remove dublicate.
so iam asking u if who is right me or them and if u can tell yr comments
thanx a lot
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Apr 24, 2000
Hi,
Can anybody of u guyz help me out of this. I transferred my tables(about 250) to another server using DTS. But all my keys got dropped. I tried using Replication and still the destination is without my keys. What i need to do get my keys? Do i need to take a script of my keys and execute it there in destination server? If so, everytime i need to do that? Please help me out in these problem..
I really appreciate any help amidst your precious schedule..
Thank you very much
Rose, Shania
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Nov 15, 2006
"Violation of PRIMARY KEY of restriction 'PK_Approve_Overtime'. The overlapping key cannot be inserted in object 'Dbo.Approve_Overtime'. The statement was ended."
can soemone explain to me why i have this kind of error?
i have this two tables. approve_overtime table has a primary key id_no and application_input table with a primary key of id_no!
all the values from of application_input will be stored also in approve_overtime.
sometimes the datas can be stored.sometimes it cannot and produces an error!
what do u think?
hmmm pls help!
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Apr 17, 2007
Can any body tell me how to know to what columns of other table it refers to.
shiva kumar
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Apr 3, 2008
Hi,
I am currently playing with Sql Express 2005, and I am wondering if there is any way to create secondary keys on a table?
I know you can create compound Primary Keys (not sure that is the correct terminology), and Foregin Keys. However, I am unsure about secondary keys ( compound or otherwise).
Could someone tell me if this is possible. I am looking at migrating from an Acucobol Vision file system, which makes heavy use of secondary keys.
Cheers
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May 16, 2002
Using SQL Svr 7.0. It appears that primary keys are created as nonclustered
unique indexes. Is there a configuration setting I can use to make them be
created as clustered unique indexes?
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Apr 4, 2001
If a table has a column defined as Int, Identity(1,1) which is to be used as the primary key, should that index be defined as clustered or non-clustered? In Enterprise manager when you create a PK on a table it defaults to being a clustered index. I am sure the answer depends on the other index requirements and columns in the table but I'd like to see what other ppl think about this.
Thanks!
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Mar 14, 2000
I have read that SQL Server tables can't have more than one primary key. I know in Access two keys are allowed. Why can't there be two primary keys in a single table in SQL Server 7.
Thanks
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Aug 24, 1999
Could someone enlighten me as to the advantage of using the foreign key tab when in table design mode in the Enterprise Manager. Does it have any advantages ?? Is it necessary ??
thanks in advance
Paul
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Mar 29, 2001
I haven't tried, but does anyone know if its possible to a have a foreign key for two tables when the tables reside in different databases (on the same server)?
Thanks,
Doug Smith
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Oct 25, 2001
l'm trying to do inserts on tables with foreign keys and they keep crashing. Can somebody please help.Whats the best way of populating data that has foreign keys?
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Jun 15, 2004
Hi everyone,
Does someone knows how can I drop a primary key (that I don't know the name) from a table in one sql statement.
Thanks,
Fady
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