From: Johan De Meersman (vegivamptuxera.be)
Date: Thu Apr 22 2010 - 06:24:27 CDT

• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

The count happens after the where on an index - it should just count the
appropriate index rows without looking at the values. Worth benchmarking on
your dataset, though.

On Thu, Apr 22, 2010 at 1:22 PM, Aveek Misra <aveekmyahoo-inc.com> wrote:

> How can count(*) in an InnoDB table be faster than MAX() considering that
> the former needs to do a table scan and the latter can use an index if
> correctly used? My code starts the sequence from 1.
>
>
> Thanks
> Aveek
>
> Johan De Meersman wrote:
>
>> Kudos for managing to drag up such an obscure piece of functionality :-) I
>> can see where it would be useful, though.
>>
>> As to your question, though: given that that page indicates that it will
>> reuse deleted sequence numbers, I think your best bet would be select id :=
>> count(*)+1 from table where cluster='clusterA' AND file='fileA' ; - should
>> be slightly faster than a max(), I think. That in a trigger on your table
>> should emulate the behaviour pretty closely.
>>
>> Am I mistaken, or does your code try to start from sequence 0 ?
>>
>> --
>> Bier met grenadyn
>> Is als mosterd by den wyn
>> Sy die't drinkt, is eene kwezel
>> Hy die't drinkt, is ras een ezel
>>
>
>
> --
> MySQL General Mailing List
> For list archives: http://lists.mysql.com/mysql
> To unsubscribe: http://lists.mysql.com/mysql?unsub=vegivamptuxera.be
>
>

--
Bier met grenadyn
Is als mosterd by den wyn
Sy die't drinkt, is eene kwezel
Hy die't drinkt, is ras een ezel

• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]