[OT] large db question about no joins

Daniel Fetchinson fetchinson at googlemail.com
Thu Apr 16 20:45:49 CEST 2009


[off but interesting topic]

Hi folks, I've come across many times the claim that 'joins are bad'
for large databases because they don't scale. Okay, makes sense, we
agree. But what I don't get, although I watched a couple of online
videos on this topic (one by the creator of flickr who gave a talk at
djangoconf and another one by a dev guy from facebook, I think the
links were posted here too) is how do people solve most basic problems
without joins? I guess the whole database layout has to be designed
with this in mind but suppose I have the following layout, how would I
redesign it so that I can have the same functionalities?

Let's say I have a table called zoo, another one called cage, another
one called animal and another one called leg. Each animal has some
number of legs, each cage has animals in it and each zoo has a number
of cages in it. Obviously these are represented by foreign keys. If I
need the total number of animals in a zoo, or the total number of legs
in the zoo I would use a query with join(s).

What would be the corresponding database layout that would scale and I
could get the total number of legs in the zoo or total number of
animals in the zoo without join(s)?

Cheers,
Daniel

[/off but interesting topic]

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