Re: An 1-to-1 relation: Is it normal?

Igor,

The solution you propose is usually applied to the situation where you have two or more sets of columns which might apply to the overall entity. For example: Person, Employee and Client. Now a Person may be an Employee, a Client, both, or neither. In this case three tables would be used, with Person being the parent and Employee and Client being 'weak entities' of Person. This means that Employee and Client would have as their PK a FK reference to Person. Attributes common to all entities would be kept in the Person Table.

To move all optional fields to a separate table would only make sense if in most cases *none* of those fields were applicable. Since any record in the dependant table will take up the same space whether one or more of it's fields are filled. In addition, your reports and displays will probably want to display any possible information in these optioal fields. This will mean that you will need to use a 'left outer join' for all your select statements, which may not be as efficient as extracting the information from a single table. (I'm not sure about the overhead associated with this type of operation in Oracle, if any).

Regards, David. Received on Tue Mar 31 1998 - 00:00:00 CST