Edit: I hate the way I had to format this document for this blog post. If you want this tutorial better formatted, check out the Word document.

One-to-Many Relationship

Logical

On ER/Studio, two tables are created. The Store table has a primary key StoreID. The Manager table has a primary key, ManagerID and a foreign key, StoredID (which is mapped to StoreID from the Store table).

Physical

On SQL Server, two tables are created. The Store table has a primary key StoreID. The Manager table has a primary key, ManagerID and a foreign key, StoredID (which is mapped to StoreID from the Store table).

Manager Table:

If you allow NULLs for StoreID in the Manager table, then you’ll be able to have a Manager without a store. If you don’t allow NULLs (leave it unchecked), then you’ll have to have at least one Store assigned to a Manager.

Querying

The above states that one store can have many managers. Here’s some sample data what’s in the tables:

SELECT * FROM Manager

SELECT * FROM Store

Get all manager information with for all managers that belong to a store:

SELECT Manager.ManagerID, Manager.FirstName, Manager.LastName, Manager.StoreID, Store.[Name], Store.Address, Store.STATE, Store.City, Store.Zip FROM Manager INNER JOIN Store ON Manager.StoreID = Store.StoreID

Get all manager information with for all managers (even if they don’t have a store):

SELECT Manager.ManagerID, Manager.FirstName, Manager.LastName, Manager.StoreID, Store.[Name], Store.Address, Store.STATE, Store.City, Store.Zip FROM Manager LEFT OUTER JOIN Store ON Manager.StoreID = Store.StoreID

Notice the NULL for Steamboat Willie. He doesn’t have a store, so all Store related fields show as NULL.

Many-to-Many Relationship

In order to implement this physically, you need a join table. In this case, we use StoreManager. Logically, you only need only two entities (Store and Manager).

Logical

Physical

On SQL Server, three tables are created. The Store table has a primary key StoreID. The Manager table has a primary key, ManagerID. The table StoreManager has two foreign keys:  StoredID (which is mapped to StoreID from the Store table) and ManagerID (which is mapped to the ManagerID from the Manager table).

StoreManager Table:

If you allow NULLs for StoreID and ManagerID in the StoreManager table, then you’ll be able to have a Manager without a store. If you don’t allow NULLs (leave it unchecked for both), then you’ll have to have at least one Store assigned to a Manager.

Here’s some sample data what’s in the tables:

SELECT * FROM Manager

SELECT * FROM Store

SELECT * FROM StoreManager

Get all manager information associated with his store:

SELECT  Manager.ManagerID,  Manager.FirstName,  Manager.LastName,
        StoreManager.StoreID, StoreManager.ManagerID, Store.StoreID,
        Store.[Name],Store.Address, Store.STATE, Store.City, Store.Zip
FROM    Store
        INNER JOIN StoreManager ON Store.StoreID = StoreManager.StoreID
        INNER JOIN Manager ON StoreManager.ManagerID = Manager.ManagerID