Re: How to find Brothers and Sisters?

Neo a écrit :

> > This view gets the id of the parent for a specific sibling...
> > create view as Q_B
> > SELECT DISTINCT person.id
> > FROM link INNER JOIN person ON link.child = person.id
> > WHERE (((person.name)='John'))
>
> To get John's parent's id, shouldn't the query select link.parent
> instead of person.id?
>
> > This view gets all sibling's for a specific parent id then restricts name ...
> > select P2.name from person P2
> > inner join link
> > on Q_B B
> > on P2.parent = B.id
> > where P2.name <> 'John'
>
> P2 is an alias for person table, so P2.parent is really person.parent,
> but the person table doesn't have a parent field (link table does)?
> Also is joining person and link tables based on Q_B valid?
Setting up hierarchies on a relational perspective is not a difficult thing to do. Putting a parent attribute in person does not allow to have a 1:0 cardinality between person and sibling , a common error done...A person does not nessecarily have a parent while may or may not have a sibling...In other words there is only one correct way to do that RM wise... Received on Sun Dec 03 2006 - 22:00:33 CET