In the EER model there are subclasses entities. I was wondering what's the way to implement that in a real SQL Table or if there is any guide that might help me out to understand how to implement entities subclasses into tables that would help. Thanks
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Martin Fowler's book Patterns of Enterprise Application Architecture covers solutions for subclassing tables:
These correspond to the options in the answer from @spencer7593, without being tied to Java & Hibernate.
Bill Karwin
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+1. This is a better answer than my answer. (No one likes to be tied to Hibernate, but the documentation is invaluable if you are tied to it.) – spencer7593 Jul 24 '13 at 19:37
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The Hibernate documentation has discussion of the options available for representing inheritance hierarchies in a relational database. There are undoubtedly better tutorials, but the Hibernate ORM (love-it-or-hate-it) wrestled with this problem.
Because there is no single "best way" to represent an inheritance hierarchy, they support all the options:
table per class hierarchy - basically one table, with all the attributes from all the subclasses. lots of columns will likely be null on lots of rows
table per subclass - one table for the superclass, and a separate table for each subclass
table per concrete subclass - separate table for each subclass (no table for superclass)
There's no single right answer. Each of these approaches benefits and drawbacks.
http://docs.jboss.org/hibernate/orm/3.3/reference/en-US/html/inheritance.html
spencer7593
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+1 Yep, Hibernate is a concrete implementation of these patterns, and if the OP is using Java, it's very relevant. – Bill Karwin Jul 25 '13 at 00:20