March 2nd, 2010
Many-to-Many Relationships
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A. Relational Database Basics
In a many-to-many relationship, each row in Table A can have zero, one, or many matching entries in Table B and Table B can have zero, one, or many matching entries in Table A. There are two ways to create a many-to-many relationship:
> Two tables can be joined together. See JOIN.
> You can create a third table called a junction table whose primary key is a composite of the keys from Table A and Table B. This creates a unique key for the junction table and changes these keys to a one-to-many relationship.
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