Duplicate Foreign Keys.

Oct 30, 2006

Hi all,

SQL server allows to create as many as foreign key constraints on a same table for a same column.

Will this affect the design or performance in anyway ?

Naming the constraint would be a good way to avoid this.But in case if someone has already created, How do I remove the existing duplicate keys ?

======================
For Example , I have 2 tables Author and Book. I could execute the below query n times and create as many as foreign keys I want.

ALTER TABLE Books
ADD
FOREIGN KEY (AuthorID)
REFERENCES Authors (AuthorID)

======================

Thanks is advance,

DBAnalyst

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Finding Duplicate Foreign Keys

May 29, 2007

Hi

i tried the following query and able to get the list of foreign keys with column names as well as referred tables and referenced column

select parent_column_id as 'child Column',object_name(constraint_object_id)as 'FK Name',object_name(parent_object_id) as 'parent table',name,object_name(referenced_object_id)as 'referenced table',referenced_column_id
from sys.foreign_key_columns inner join sys.columns on (parent_column_id = column_id and parent_object_id=object_id)
Order by object_name(parent_object_id) asc

but i am not able to get the fks created more than once on same column refering to same pk

Thanks in Advance

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Creating Inter-table Relationships Using Primary Keys/Foreign Keys Problem

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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Creating Indexes On Columns That Are Foreign Keys To Primary Keys Of Other Tables

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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Nov 22, 2007

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Apr 17, 2007

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Mar 29, 2001

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Oct 25, 2001

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Oct 4, 2004

How would I drop a foreign Key?

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Mar 10, 2004

I need to know if this is required? I have products, with the help of their business account numbers, are naturally categorized numerically. I want to create a product category table and a product account table.


Example :
tbProductCategories
TypeCode | Description
1000 | Cups
2000 | Plates

tbProductAccounts
Account | Description
1001 | Mug
1002 | Glass
2001 | Plate
2002 | Saucer


With the above tables (which are made up :) ), would you include
a foreign key in tbProductAccounts indicating the type code?

What would the stored proc look like without it?


Create Procedure usp_GetProductAccounts

@iTypeCode int

AS

SELECT tbProductAccounts.Account,
tbProductAccounts.Description
FROM tbProductAccounts
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Would this work? Or should the foriegn key always be included?

Mike B

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Foreign Keys - Allow Zero?

Jun 8, 2008

I am creating a series of foreign keys in my new database, and so far everything is going fine. The company I work for never uses them, and I am working on my own stuff on my own time now.

I come across one table that I do want one field to allow zeroes, but when its set to a value, to exist in the other table.

To be more specific. I have a PO type table, which has an EmployeeID of the person who made the PO, and another field to store who received the PO when the order arrives. I want that 2nd Employee field to be zero until it's received.

I created an employee of zero, to allow the foreign key to be created. But all the other tables that have foreign keys to my Employee table I would prefer to not allow zeroes. So I changed them to use a check of (employeeid > 0).

Is it possible to have a foreign key say that I want the value from the Field in Table A to exist in table B, or to be zero? Or would it just be easier to leave off the foreign key in this one case?


Tks

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Foreign Keys

Dec 15, 2006

Shiry writes "Hi, I'm a beginner and I'm a bit stuck here..

I'm creating this database for my homework, I'm using Marks & Spencer as an
example. It has a table, products, for the clothes

id
name
cat_id ....... connected to typ_cat
colour_id ...... connected to typ_colour
size_id ....... connected to typ_size
price
sup_id ....... connected to typ_sup ...... but here i'm stuck a bit, are you
allowed to connect a typ_table to another typ_table?

this is the typ_sup:
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name
address
city_id ......... connected to typ_city

or rather have a separate sup table with the same id, name, address, city_id
id will be connected to typ_sup
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What way is better? and is it allowed to connect a typ_table to another
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Thanks in advance!!!!

Shiry"

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Foreign Keys

Oct 11, 2006

I have created two tables:

UserInfo:

UserID (PK)

Hairid

eyeColorid

faceShapeid



and

HairInfo:

HairInfoID (PK)

Hairid

HairDesc

Now I want to have a one to many relationship between UserInfo and HairInfo. I want to specify Hairid as the foreign key in the HairInfo table. Here UserInfo is the parent and HairInfo is the child. I am using SQL server 2000. Is there a way to do it using the Enterprise manager interface. Can someone run me through the steps to do it.

Thanks...



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Feb 28, 2008

Is there a way to temporaly set off foreign keys dependencies (like a sql command or something...) and then set them on again? I've to migrate 90 tables on my app, but i get the "dependencies error", any ideas?

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Mar 24, 2008

having been used to creating databases for the past nine years in MS Access, i have been recently getting used to the basics of SQL Server 2005 express edition. i know pretty much all of the simple basics, but i have hit some trouble.

in MS Access, when i have used the "Design View" to develop all of my tables, fields and validation rules, i have used their "Lookup Wizard" to develop ways of assigning a record to a certain value - example;

CLUB:
Club_Id (Primary Key)
Club

PLAYER:
Player_Id
Player_Name
Club (Foreign Key)

the flaw, i suppose, is the ease with which i can create a relationship between TWO tables without the child tables foreign key having to be an ID (integer) and users can select a "Club" of their choice to assign a "Player" to in the PLAYER table. i.e.

CLUB:
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Club: Man Utd

PLAYER:
Player_Id: 1
Player_Name: Ryan Giggs
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instead of;

PLAYER:
Player_Id: 1
Player_Name: Ryan Giggs
Club: 1 (FKEY)

i hope i am making sense. now the awkward bit as far as i'm concerned:

in SQL Server 2005 Management Studio Express, i cannot do this once i do the necessary tables, content and relational diagrams.

so i have this;


PLAYER:
Player_Id: 1
Player_Name: Ryan Giggs
Club: 1 (FKEY)

instead of what i want, which is this;


PLAYER:
Player_Id: 1
Player_Name: Ryan Giggs
Club: Man Utd (FKEY)

how can this be achievable using Studio Management Express 2005 for someone like myself who is still something of an SQL novice (of a sort)

help would be much appreciated

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Remote Foreign Keys

Jun 21, 2007

Right now i'm building a language centre DB. Is going to hold translations for data in tables in another DB (english DB). The idea is going to be that there is going to be a table in the Language DB for every language and table it is going to translate in the english DB.
So lets consider the following in the English DB:
PROJ_TBL_HELPTOPICS  -> PK_HELP_ID -> TITLE -> DESCR
PROJ_TBL_CATEGORIES -> PK_CAT_ID -> TITLE -> DESCR
 
In the Language DB I want to hold translations for HELPPTOPICS and CATEGORIES, and I want translations for Spanish and Japanese.
PROJ_TBL_HELPTOPICS_ES -> PK_TRANS_ID -> FK_HELP_ID -> TRANS_TITLE -> TRANS_DESCR
 
The rest is going to be the layout as abovePROJ_TBL_HELPTOPICS_JA PROJ_TBL_CATEGORIES_ESPROJ_TBL_CATEGORIES_JA
The reasons I separated up the language DB from the english DB are:
1. English DB has, and is going to have a lot more tables, and is going to be heavily queried (plus I think dont think the translations are going to be used anywhere near as often and the english). I figured the less tables, where possible, the better.
2. Putting translations in different a different DB, I could take better advantage of colliations specific to a language for example when using Full-Text searching on Japanese text
 
Anyways, here's my question!?!
I want to link the foreign key column to the table it is translating primary key column (in the English DB). I want to be able to take advantage of Cascade on Delete. So when an item is deleted from EnglishDB.PROJ_HELP_TOPICS it is going to be deleted from LanguageDB.PROJ_HELP_TOPICS_[LANG ISO]. Is this done through Mirroring?

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Jan 7, 2008

hi.
How to update FormA table from customer table. Let say i wish to keep small number of fields from each table so i use foreign keys as reference.
However i had a problem when i tried to save the relationships of both tables, i receive the error that FormA_id is not able to insert null into value.
Cust_id(PK) is identify column, as well FormA_id(FK) and FormA_id(PK) too. For example, when i insert a record from customer table, it will automatically create id for FormA.
Table structure. Customer
cust_id(PK),name,age,formA_id(FK)
Table structure, FormA
formA_id(PK), info, date,
How to solve ?

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Feb 3, 2008

I'm working with a SQL 2000 DB, which has a table structure as follows, implemented with foreign key constraints: ________________________________|                                                        ||--> TABLE1 --> TABLE2 --> TABLE3 --|
 (ie, it forms a 'loop' so to speak)
I am trying to create a clean copy of this database, basically by deleting all the data in most of the tables, and these 3 tables are included. Of course, when I run a DELETE on any of these tables, it complains because of the FK. How can I script a delete on the 3 tables without manually deleting row after row, until there aren't anymore relations?
Cheers for any help :)

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Feb 1, 2004

Hi everyone,

I've been using VS.NET to design and implement my SQL databases. This has been simple and effective.

I've deployed the database onto the production database server and it's been performing without a hitch for some time now.

My problem is that I now need to remove a foreign key relationship on the production database as I have had a relationship between two tables but now not wanting the relationship since the data that had the relationship is now not wanting to be compulsory. I've had a look in the system.foreignkey (I think) table but I can't make head or tail of it.

Long story short, how can I find and remove the relationship from Query Analyser / Enterprise Manager ? I know how to do this in VS.NET diagram (just delete the relationship) but when you open the production database in VS.NET the diagram is no longer there.

Any help will be appreciated!!

Thanks!
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Sep 4, 2005

Hey all - been knocking my head on this on for awhile - perhaps someone could shed a little light.
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First Name
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Table 2:
AuditionID - PK
Description
Sing
instrument

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I hope I am being clear enough - any help would be greatly appreciated.

Thanks all

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Aug 25, 1998

Hi!
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Msg 547, Level 16, State 2
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HELP!!!!
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Jan 14, 2005

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So I have a table of states (that doesn't need maintaining) and a table of regions (that does. New regions could be added, existing regions could be modified.)

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stateCode char(2),
stateName varchar(16),
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)

CREATE TABLE regions (
regionId int primary key,
regionCode char(6),
regionName varchar(32),
UNIQUE(regionCode)
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My table of items points to these other tables. I want to use foreign keys for referential integrity. So my table looks something like this:

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itemId int primary key,
itemName varchar(32),
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areaNum int,
stateId int NULL,
regionId int NULL,
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UNIQUE(areaNum, stateId, regionId),
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FOREIGN KEY regionId REFERENCE regions (regionId)
)

My problem seems to be that when I insert records into the items table, MS SQL doesn't like a foreign key entry to be null (even though I say it can be null.) I think the problem is that there is no value in the states or regions table with the stateId/regionId = 0. I don't want to entry a dummy entry for a non-state or non-region, but I can't figure out how to do this otherwise.

Is there a way to have MS SQL permit a foreign key value to be NULL? Or is there a better way to organize this data? I would appreciate any guidance. Thanks.

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Aug 2, 2004

I've posted this in the general database forum as well but think it is more sql server specific. I have three tables as below. My problem is that when I insert anything into has_quote, cat_ref and cust_id are both null. Any ideas on how to get round this? Thanks


Code:

CREATE TABLE Item (
cat_ref INT IDENTITY(1,1) PRIMARY KEY,
descrip VARCHAR(50),
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cat_type VARCHAR(20),
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supplier_name VARCHAR(20),
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commercial_markup SMALLMONEY,
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cat_ref INT FOREIGN KEY
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Jun 25, 2004

What are the possible issues I could run in to having multiple foreign keys in a table. Here is why I ask. I have a db (sql server) that has a participant table, a forum table, and a forum reply table. Every record in the forum reply table is associated with the forum table via a PK-FK relationship w/cascading updates/deletes. The participants who post in these tables are not tied back to the participant table via a PK-FK relationship w/cascading updates/deletes. Should they be?

The problem I ran in to is that one particpant was deleted from the participant table but a post with their partid still existed in the forum or forum reply tables.

My feeling is that anytime a participant is deleted, everything that pertains to them should go too, right? If I am right, what do I have to be careful of if I do that?

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Nov 20, 2004

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Dec 30, 2004

I am having trouble creating multiple foreign keys on a table so that I can set up cascading update and cascading delete from two different primary tables. I am using the diagram to do this but when I try to save the diagram I get the following error.



ODBC error: [Microsoft][ODBC SQL Server Driver][SQL Server]ALTER TABLE statement conflicted with COLUMN FOREIGN KEY constraint 'FK_IndResults_RaceData'. The conflict occurred in database 'VIRA', table 'RaceData', column 'RaceID'.



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Thanks!

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Hi all

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