| From: | David Johnston <polobo(at)yahoo(dot)com> |
|---|---|
| To: | Phoenix Kiula <phoenix(dot)kiula(at)gmail(dot)com> |
| Cc: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, PG-General Mailing List <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Table Design question for gurus (without going to "NoSQL")... |
| Date: | 2011-11-21 03:17:49 |
| Message-ID: | 8283C8CD-86BB-4CE3-9E4A-0880068BDFEC@yahoo.com |
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| Thread: | |
| Lists: | pgsql-general |
On Nov 20, 2011, at 20:50, Phoenix Kiula <phoenix(dot)kiula(at)gmail(dot)com> wrote:
> On Mon, Nov 21, 2011 at 7:26 AM, Gavin Flower
> <GavinFlower(at)archidevsys(dot)co(dot)nz> wrote:
>
>> How about having 2 indexes: one on each of ip & url_md5? Pg will combine the
>> indexes as required, or will just use one if that is best.
>
>
>
> Thanks Gavin. Question: what if I have a joined index? If from a
> joined index I only use the first column (say, "ip") will a joined
> index still be used?
>
> It is cleaner to create two indexes for the two columns. Which is recommended?
>
An index on (a, b) can be used for queries involving only a but not for those involving only b.
Neither is recommended - both have their benefits and limitations.
David J.
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