AdventureWorks DB question

Hi, I have been looking at the Adventure works DB diagram and I am confused about the relationship that employees, customers and individuals has with contact i.e. a 1-1, 1-many or many-many relationship. Also why is it broken down like that.

Thanks,

Nadim.

Hi Nadim,

AdventureWorksDB is designed to show a complex data schema in a nomalized structure. AdventureWorks is probably a bit overcomplex if you're just learning about normalization, but once you understand the concepts, it becomes more clear.

Note: If you are new to normalization, you should search for a few topics about it to get the basics. You might also find the Northwind or Pubs sample databases to be a bit more understandable. You can download either from http://www.microsoft.com/downloads/details.aspx?FamilyID=06616212-0356-46a0-8da2-eebc53a68034&DisplayLang=en. They are SQL 2000 samples, but they will still work in 2005.

On to the description...

If you look at the fields in each of the tables, you'll see that the Contact table contains the base information about a person, e.g. first name, last name, phone, etc. The Contact table is linked to both the Employee and Individual tables. Both Employees and Individuals are types of people that have special properties in addition to the base person information stored in the Contact table. So an Employee has a ManagerID and LoginID, but an Individual doesn't. Because of the relationship between Contact and Employee, there is no need to store the first name, last name, etc. in the Employee table, it is retrieved through a join.

If I wanted to get a list of Employee names, with Titles and Hire Dates, I'd need to write a query that uses both the Contact and Employee table, as follows:

SELECT C.FirstName, C.LastName, E.Title, E.HireDate
FROM Person.Contact C INNER JOIN HumanResources.Employee E
ON C.ContactID = E.ContactID

The relationship with Individual is similar, only it extends through Individual onto Customer. Each Customer has an Individual associated with it, and that Individual, is a person who has Contact information. I'll be honest, I don't really know why they split Customer and Individual, it could have something to do with the way they wanted to use the data being stored.

Hopefully that brings a little light to the subject.

Regards,

Mike Wachal
SQL Express team

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