Re: Automatic optimization of IN clauses via INNER JOIN

On Thu, Dec 17, 2009 at 6:05 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Dec 17, 2009 at 10:23 AM, Thomas Hamilton
> <thomashamilton76@yahoo.com> wrote:
>> Apparently the latest version of MySQL has solved this problem:
http://www.xaprb.com/blog/2006/06/28/why-large-in-clauses-are-problematic/
>>
>> But I am running PostgreSQL v8.3 and am observing generally that SELECT ... WHERE ... IN (a, b, c, ...) is much
slowerthan SELECT ... INNER JOIN (SELECT a UNION ALL SELECT b UNION ALL SELECT c ...) 
>
> That's certainly not MY observation.  It would be interesting to see
> what's going on in your case but you'll need to provide more details.
>
> http://wiki.postgresql.org/wiki/Guide_to_reporting_problems
>

I asked the same question many times, and answer was always the same -
there's no point in doing that...
well... I've been asked by folks at work, the same thing (for typical
engineer, grasping the idea of join can be hard sometimes...).




--
GJ