SQL efficiency argument, add a column or solvable by query?

Posted by theTurk on Stack Overflow See other posts from Stack Overflow or by theTurk
Published on 2010-03-29T14:02:40Z Indexed on 2010/03/29 14:53 UTC
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I am a recent college graduate and a new hire for software development. Things have been a little slow lately so I was given a db task. My db skills are limited to pet projects with Rails and Django. So, I was a little surprised with my latest task.

I have been asked by my manager to subclass Person with a 'Parent' table and add a reference to their custodian in the Person table. This is to facilitate going from Parent to Form when the custodian, not the Parent, is the FormContact.

Here is a simplified, mock structure of a sql-db I am working with. I would have drawn the relationship tables if I had access to Visio.

We have a table 'Person' and we have a table 'Form'. There is a table, 'FormContact', that relates a Person to a Form, not all Persons are related to a Form. There is a relationship table for Person to Person relationships (Employer, Parent, etc.)

I've asked, "Why this couldn't be handled by a query?" Response, Inefficient. (Really!?!)

So, I ask, "Why not have a reference to the Form? That would be more efficient since you wouldn't be querying the FormContacts table with the reference from child/custodian." Response, this would essentially make the Parent is a FormContact. (Fair enough.)

I went ahead an wrote a query to get from non-FormContact Parent to Form, and tested on the production server. The response time was instantaneous. *SOME_VALUE* is the Parent's fk ID.

SELECT FormID 
FROM FormContact 
WHERE FormContact.ContactID 
    IN (SELECT SourceContactID 
        FROM ContactRelationship
        WHERE (ContactRelationship.RelatedContactID = *SOME_VALUE*) 
            AND (ContactRelationship.Relationship = 'Parent'));

If I am right, "This is an unnecessary change." What should I do, defend my position or should I concede to the managers request?

If I am wrong. What is my error? Is there a better solution than the manager's?

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