| From: | Rod Taylor <rbt(at)rbt(dot)ca> |
|---|---|
| To: | Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au> |
| Cc: | Antti Haapala <antti(dot)haapala(at)iki(dot)fi>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Multicolumn foreign keys need useless unique indices? |
| Date: | 2002-09-13 11:27:17 |
| Message-ID: | 1031916438.15720.10.camel@jester |
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| Lists: | pgsql-hackers |
On Fri, 2002-09-13 at 04:27, Christopher Kings-Lynne wrote:
> > AFAIK, the extra index only slows down my inserts - it basically contains
> > no usable information...
>
> Not 100% true. It will speed up cascade delete and update...
>
> > shouldn't the presence of _primary_key_ in
> > multicol foreign key be enough to decide whether the whole key is unique
> > or not?
>
> Hmmm - thinking about it, I don't see why postgres would need the entire
> thing to be unique...can't think of a reason at the moment. Stephen?
If it's not all unique, you cannot be guaranteed there is a single row
with those values in the referenced table.
--
Rod Taylor
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