Message-ID: <44B2CFC7.7060101@obviously.com>
Date: Mon, 10 Jul 2006 15:08:07 -0700
From: Bryce Nesbitt <bryce1@obviously.com>
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.13) Gecko/20060411
MIME-Version: 1.0
CC: pgsql-sql@postgresql.org
Subject: Re: Can function results be used in WHERE?
References: <44B29376.2030107@obviously.com>
	<bf05e51c0607101302w271c7773tdec47e76b192f2c9@mail.gmail.com>
In-Reply-To: <bf05e51c0607101302w271c7773tdec47e76b192f2c9@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

Aaron Bono wrote:
> First I recommend making your function IMMUTABLE since, given the same
> arguments, it gives the same result - this will allow PostgreSQL to
> optimize the function call and cache the results. 
Will do!

> Then, don't use "4", use "calculate_distance(lat,lon,
> 37.789629,-122.422082)".  That use is very ambiguous and subject to
> breaking if you change the columns in your select.  It may also be the
> reason you have a problem though I don't use that syntax so cannot be
> sure.
I think it is ugly also, but no other syntax seems to work:

stage=# select
pod_code,lat,lon,calculate_distance(lat,lon,37.789629,-122.422082) as
dist from eg_pod where dist < 1 order by dist desc limit 10;
ERROR:  column "dist" does not exist

stage=# select
pod_code,lat,lon,calculate_distance(lat,lon,37.789629,-122.422082) as
dist from eg_pod where 4 < 1 order by dist desc limit 10;

 pod_code |    lat    |     lon     |       dist
----------+-----------+-------------+------------------
       20 |         1 |           1 | 7962.56837300854
       36 |  37.39424 | -122.077673 | 33.2296275931303
       45 | 37.426929 | -122.161922 | 28.8542985664155
       44 | 37.422813 | -122.172403 | 28.8253772580912
       22 | 37.444638 | -122.156875 | 27.9378660315883
       34 | 37.875915 | -122.257427 | 10.7947710258918
       81 | 37.903325 |  -122.29963 |  10.323500058406
       33 | 37.868001 | -122.261818 | 10.2977353566856
       17 | 37.873002 |  -122.26968 | 10.1277713471574
       14 | 37.869574 | -122.267937 | 10.0742861708283
(10 rows)


> The only difference between HAVING and WHERE is that WHERE occurs
> before a GROUP BY and HAVING occurs after.  Since you have no GROUP BY
> there should be no difference in the queries.  The only other
> difference is the "4 > 5::double precision" so that is where I would
> start.
WHERE does nothing in my example.
HAVING filters the results according to distance.
So there's got to be more to it.


-- 
----
Visit http://www.obviously.com/