Subject:
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Re: A heirarchical database question
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Thu, 16 Nov 2000 20:11:24 GMT
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Viewed:
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350 times
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In lugnet.off-topic.geek, Jim Hughes writes:
would be the best way to describe it in a DB table? Would this work OK:
>
> -----------------------------------
> Big table of Themes
>
> theme_parent (varchar)
> theme_name (varchar)
> theme_child(varchar) <-- this is actually a GRANDCHILD of the theme_parent!!
> -----------------------------------
You don't want to use both parent and (grand) child in the same table. It
won't work, or it will introduce unneeded redundancy.
You can either model hierarchy in the same table that you keep the rest of
the theme data in, in which case, use a parent link from the theme upwards
(and no child, else you are saying that all themes have only one child)....
or you can model this in a separate relation table.
In that case, keep both the parent and child (in this case it's a child, not
a grandchild) in that separate table.
That makes relation traversal relatively quick. My experience with this in
the past has been that even with deeply nested relations, the performance
hit of having a separate relation table is way offset by the flexibility (it
becomes much easier to reorder the tree)
Keeping full paths in the main table is doable, but introduces overhead and
data redundancy. a query to derive the full path in either organization is
easy to write and runs quite quickly.
(I don't like redundancy in database designs, it causes data staleness and
introduces errors)
++Lar
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Message has 1 Reply:
Message is in Reply To:
 | | A heirarchical database question
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| Hi: Here is a question for the DB experts: Say you had some data that was heirarchical, e.g. a list of Lego Themes: -- System ----- Aquazone ---...--- Aquasharks What would be the best way to describe it in a DB table? Would this work OK: ---...--- (...) (24 years ago, 15-Nov-00, to lugnet.off-topic.geek)
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