Question

I’m trying to create 2 tables in Visual Studio server pane and I have a problem creating the foreign keys.

When I’m trying to create them in the relationship page it won’t let me create foreign keys until I make them primary keys.

I don’t understand why I can’t have a different member in my table that it is primary key and a different one a foreign key.

My tables are like this:

Table People:

Primary key: ID int
             Name nvarchar
             Age int
             City nvarchar
Foreign key: AccountNumber int  --> when I make him primary key everything works.

Table BankAccount:

    
Primary key and Foreign Key: AccountNumber  int
                             Money float

ps.
I used some mysql with CMD and I remember that I could do this, but because I don’t have this control in visual studio I’m lost.

UPDATE:
Rup made a good point that i only relize afther answering the qustion he ask me
i just did the realtionship (Foreign Key) for the bank account table and now i got
what i wanted thank you!

Answer 1

Why is BankAccount.AccountNumber a Foreign Key? Are you trying to reference back to the the person who owns it?

If that is the case, BankAccount should be:

CREATE TABLE BankAccount
(
   AccountNumber int PK,
   Money float,  // bad idea.  Use currency or int (i.e. store balance as pennies)
   Owner int FK REFERENCES People.ID
)

And drop the account ID from the people table.

This models the relationship “an Account has 1 and only one owner” and allows the relationship “A person can have many accounts.”

It looks like what you’re trying to do is create a back reference. If you were to choose to do this, then the back reference to the owner should be on People.ID, not on account. — Although this is unnecessary because you can simply query

SELECT * FROM
BankAccount INNER JOIN People ON BankAccount.Owner = People.ID

to get all accounts and their owners.

If you want to establish multiple owners for an account, AND many accounts per user, then you need to establish a third table to implement the many-to-many relationship.

CREATE TABLE AccountOwners
(
   AccOwnID int PK,
   AccountID int FK REFERENCES BankAccount.AccountNumber,
   PeopleID int FK REFERENCES People.ID
)

And drop the People.AccountNumber and BankAccount.Owner. This technique is akin to maintaining a list of all accounts and owners which you can query.