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Is a Junction-Table basically just the table that sits between two entities that have a M-M relationship?

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2 Answers 2

up vote 8 down vote accepted

A junction table is a weak entity, but a weak entity often is not a junction table. A junction table is not the same as a weak entity. A junction table is a type of weak entity.

Tables used to resolve repeating groups are also weak entities. These are only junction tables if the repeating group contains a repeated foreign key relationship.

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Should this read, "...but a weak entity may not be..."? – Air Dec 18 '13 at 22:34
@AirThomas I believe may not would imply likely is which I did not want to do. Similarly I would state A coin may be a quarter rather than A coin may not be a quarter. – BillThor Dec 19 '13 at 1:07

Depends how you define a "junction table". ER terminology tends to be somewhat ambiguous when used to describe relational database concepts.

A junction table typically means or can mean any table with two or more foreign keys.

A weak entity on the other hand is represented by a table whose primary key includes at least one foreign key attribute. That doesn't have to be the case for a junction table (i.e. a table with more than one foreign key).

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