Getting the output of a function used in a where clause

<div class="Section1"><p class="MsoNormal"><span class="EmailStyle15"><font color="black" face="Arial" size="2"><span
style="font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:
Arial">HI,</span></font></span><p class="MsoNormal"><span class="EmailStyle15"><font color="black" face="Arial"
size="2"><spanstyle="font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family: 
Arial"> </span></font></span><p class="MsoNormal"><span class="EmailStyle15"><font color="black" face="Arial"
size="2"><spanstyle="font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family: 
Arial">I’m a newbie so please bear with me. I have a function defined (got it from one of your threads… thanks Joe
Conway)which calculates the distance <span style="mso-spacerun: yes"> </span>between 2 zip code centeroids (in
lat,long).This thing works great. However, I want to sort my results by distance without incurring the additional
burdenof executing the function twice. A simplified version of my current SQL (written in a perl cgi) <span
style="mso-spacerun:yes"> </span>that returns a set of zip codes within a given radius is:</span></font></span><p
class="MsoNormal"><spanclass="EmailStyle15"><font color="black" face="Arial" size="2"><span
style="font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:
Arial"> </span></font></span><pre><span class="EmailStyle15"><font color="black" face="Arial" size="2"><span
style="font-size:10.0pt;font-family:Arial">$sql= “SELECT zipcode from zipcodes where </span></font></span><font
face="Arial"><spanstyle="font-family:Arial">zipdist($lat1d,$lon1d,lat,long) <=
$dist;”;</span></font></pre><pre><fontcolor="black" face="Arial" size="2"><span
style="font-size:10.0pt;font-family:Arial"> </span></font></pre><pre><fontcolor="black" face="Arial" size="2"><span
style="font-size:10.0pt;font-family:Arial">WhatI want to write is something like:</span></font></pre><pre><font
color="black"face="Arial" size="2"><span style="font-size:10.0pt;font-family:Arial"> </span></font></pre><pre><span
class="EmailStyle15"><fontcolor="black" face="Arial" size="2"><span style="font-size: 
10.0pt;font-family:Arial">$sql = “SELECT zipcode, distance from zipcodes where </span></font></span><font
face="Arial"><spanstyle="font-family:Arial">distance <= $dist order by distance;”;</span></font></pre><pre><font
color="black"face="Arial" size="2"><span style="font-size:10.0pt;font-family:Arial"> </span></font></pre><pre><font
color="black"face="Arial" size="2"><span style="font-size:10.0pt;font-family:Arial">But I don’t the magic SQL phrase to
populatethe distance variable using my nifty function. Do I need to create an output type for
distance?</span></font></pre><pre><fontcolor="black" face="Arial" size="2"><span
style="font-size:10.0pt;font-family:Arial"> </span></font></pre><pre><fontcolor="black" face="Arial" size="2"><span
style="font-size:10.0pt;font-family:Arial">Thanksin advance!</span></font></pre><pre><font color="black" face="Arial"
size="2"><spanstyle="font-size:10.0pt;font-family:Arial"> </span></font></pre><pre><font color="black" face="Arial"
size="2"><spanstyle="font-size:10.0pt;font-family:Arial">Bill</span></font></pre><p class="MsoNormal"><span
class="EmailStyle15"><fontcolor="black" face="Arial" size="2"><span
style="font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:
Arial"> </span></font></span><p class="MsoNormal"><span class="EmailStyle15"><font color="black" face="Arial"
size="2"><spanstyle="font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family: 
Arial"> </span></font></span><p class="MsoNormal"><font color="black" face="Arial" size="3"><span style="font-size:
12.0pt;font-family:Arial;color:black"> </span></font><font color="black" face="Arial"><span
style="font-family:Arial;color:black;mso-color-alt:
windowtext"></span></font></div>