Re: For the SQL Gurus out there, a question

From: Joe Weinstein <joeNOSPAM_at_bea.com>
Date: Sun, 08 Feb 2004 16:52:17 -0800
Message-ID: <4026D9C1.2090803@bea.com>

Daniel Morgan wrote:

> Anith Sen wrote:
>

>>>> All many-to-many relationships must be resolved when moving from a
>>
>>
>> logical design to a physical design. <<
>>
>> Can you explain what you mean by this? What does a many-to-many 
>> relationship
>> between two entities, which is a logical issue, have to do with physical
>> design?

>
>
> A typical many to many relationship would be ... a student can be in
> many classes and a class has many students. This is true in the
> logical model but should never be implemented in a relational database
> using two tables: Rather using three.
>
> STUDENT ... PK = person_id
> CLASS ..... PK = class_id
>
> STUDENT_CLASS (intersecting entity) ... PK person_id and class_id.

Yes. In the original post, I missed how his setup was different. It seems he has exactly that, the two tables and an association table whose two columns were the primary keys of the other two. Joe Received on Sun Feb 08 2004 - 18:52:17 CST