On 21-Jul-2001 Benjamin Pflugmann wrote:
> Hi David!
>
<snip good discussion on optimizing joins>
>
> Filesize and insertion/update speed are the main reasons. Another is
> to only use what you really need, i.e. creating indexes which you are
> not sure about using at all, should be avoided.
>
>> I use PHPmyAdmin a lot to place indexes and I also noticed that you
>> can place two indexes on the same column..??
>
> To place two keys on the same column may be possible but doesn't help
> anything.
>
> There is one exception, though, there are compound keys, which will be
> of use. So,
>
> INDEX(id), INDEX(id)
>
> makes no sense, but
>
> IDNEX(id), INDEX(id,ordernr)
>
> may make sense.
>
Benjamin, I'll pick a nit here.
A query on id only can use either index, a query on id & ordernr could
also use both indexes but the second one would be more useful.
A query on ordernr only can't use either, and will result in a full scan.
ITYM:
INDEX(id), INDEX(ordernr,id)
Regards,
--
Don Read [EMAIL PROTECTED]
-- It's always darkest before the dawn. So if you are going to
steal the neighbor's newspaper, that's the time to do it.
(53kr33t w0rdz: sql table query)
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