Re: Select Single Random Record

On Wed, Apr 18, 2012 at 09:43:23PM +0200, Petr Jakeš wrote:
> > Although this might work in the particular application, but
> > it is hardly ideal to make two queries, nor to load a long list
> > of IDs.  Is there a way to do it with a single query?
> >
> > 1)
> Is your task really "time critical"?

In my case, yes; it is number crunching.
Question should be «is it /that/ "time critical"» :-)
I have had some difficulties with slow operations due
to multiple queries, and it feels more satisfactory get
rid of any avoidable query, even if the saving is only
a fraction of a percent of the total running time.

> How many records (IDs) do you expect to be returned using the first select?

thousands in current tests;
hundreds of thousands is likely in future tests,
and millions is plausible.

> How many kb will it take? Is the list size a real problem for your Internet
> connection?

Might be; especially when it is over the Internet as opposed to
over a LAN.  Yet, I am as concerned with query processing time than
transmission time.

> How often do you expect to release the select querry?

Could vary.  About 50 clients querying once a minute each
may be typical, but I am sure I will see faster jobs completing
in seconds, in which case each client would query correspondingly
often.

> 2)
> what is your target database engine?

postgres at the moment.

> some databases allow "rand" in the select query.
> see:
> http://stackoverflow.com/questions/19412/how-to-request-a-random-row-in-sql

Ah.  Thanks for the tip.
I will look into it; obviously, I would prefer the solution to
be engine independent, but this feature might be more valuable :-)

:-- George
> 
> Petr

-- 
:-- Hans Georg

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