Re: For the SQL Gurus out there, a question

From: Daniel Morgan <damorgan_at_x.washington.edu>
Date: Sun, 08 Feb 2004 14:12:38 -0800
Message-ID: <1076278307.179016@yasure>

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.

-- 
Daniel Morgan
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damorgan_at_x.washington.edu
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Received on Sun Feb 08 2004 - 16:12:38 CST