Solved

How to add Foreign key constraint on (1:1) to (0:1) relationship in MS SQL 2005 using T-SQL/GUI?

Posted on 2008-10-02
5
3,146 Views
Last Modified: 2011-10-19
Hi, Experts,
I am new to MS SQL 2005, attached is a part of my ERD:

I don't know how to add foreign key constraint between tables: Car(1,1) and SalesInvoice (0:1) using T-SQL/GUI, can anyone help?

Also, are there any differences at all with other similar types of foreign key constraints(like, (1:1)  to (1:*) or (1:1) to (0:*)) implementing on MS SQL using T-SQL/GUI.

Thanks,
-Rick
CarDealerShip.gif
0
Comment
Question by:RHADMIN
  • 2
  • 2
5 Comments
 
LVL 37

Accepted Solution

by:
momi_sabag earned 250 total points
ID: 22621869
foreign keys in sql server are always implemnted in the same way:
a child table key is pointing to a unique / primary key at the parent
which means, that every relationship is a 1:n where n>=0
add it like this:
alter table [Sales Invoices] add constraint MyConstraintName foreign key([car id]) references car([car id])
0
 
LVL 7

Assisted Solution

by:orcic
orcic earned 250 total points
ID: 22621910
Actually, you can have 1:1 relation. You only have to make foreign key to be unique.

ALTER TABLE [Sales Invoices]
ADD CONSTRAINT SalesInvoicesUniqueCarID
UNIQUE NONCLUSTERED ([car id])
0
 
LVL 37

Expert Comment

by:momi_sabag
ID: 22621925
no
what orcic wrote will add a unique constraint
not a foreign key

you can create a unique constraint on the car id column in your table and that will make it unique
but you can't achieve a 1:1 relationship using foreign keys alone
0
 
LVL 7

Expert Comment

by:orcic
ID: 22621958
of course you need to make foreign key first and then to make it unique (that's what I ment with "You only have to make foreign key to be unique.")
0
 
LVL 1

Author Comment

by:RHADMIN
ID: 22637092
Hi, momi_sabag & orcic:

Thanks for your answers, UNIQUE constraint is what I am looking for(which I originally thought it can be done on Foreign key constraint alone somehow).
Based on the question, another question: how to set a constraints on relations like: (1:1) to (1:5)  or  (1:1) to (1:100), which means how to set minimum & maximum number of relationship check?

Many thanks,
-Rick
0

Featured Post

How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

Join & Write a Comment

International Data Corporation (IDC) prognosticates that before the current the year gets over disbursing on IT framework products to be sent in cloud environs will be $37.1B.
Ever wondered why sometimes your SQL Server is slow or unresponsive with connections spiking up but by the time you go in, all is well? The following article will show you how to install and configure a SQL job that will send you email alerts includ…
Via a live example, show how to extract information from SQL Server on Database, Connection and Server properties
Via a live example, show how to setup several different housekeeping processes for a SQL Server.

744 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now