Question

What is the best way to design a db with object types that share some columns but also have some of there own ?

Have 1 table for the shared data and let each type has its own table

[objects] o_id | o_name | object_type

[object_type_1] o_t_id | o_id | option1 | option 2

[object_type_2] o_t_id | o_id | option3 | option 4

OR
have all the columns in 1 table and have a lot of NULL’s

[objects] o_id | o_name | object_type | option1 | option 2 | option3
| option 4

Answer 1

This is a common problem. A single best solution does not exist. You’ll have to weigh the pros and cons of each always depending on your model.

Have a look at your options:

• http://martinfowler.com/eaaCatalog/singleTableInheritance.html
• http://martinfowler.com/eaaCatalog/classTableInheritance.html
• http://martinfowler.com/eaaCatalog/concreteTableInheritance.html

A different approach, for your extra properties, is EAV. This has some serious benefits but also some tremendous drawbacks, so becareful before thinking that it is the “silver bullet”:

• http://en.wikipedia.org/wiki/Entity%E2%80%93attribute%E2%80%93value_model