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<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>Bryce,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>Actually PostgreSQL 9.0+ does support ordered
aggregates</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>ST_MakeLine is a fine example that works great with ordered
aggregate syntax. e.g. ST_MakeLine(geom ORDER BY time)</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>so FIRST and LAST I envision people would probably always
want those based on some predicatable ordering. </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>I can envision cases in raster where you would want things
processed in a certain order like you want all your following rasters burned on
the first based on a certain priority of layering.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>Just my 2c.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>Thanks,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial>Regina</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=419512123-21112011><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV><BR>
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<FONT size=2 face=Tahoma><B>From:</B>
postgis-devel-bounces@postgis.refractions.net
[mailto:postgis-devel-bounces@postgis.refractions.net] <B>On Behalf Of
</B>Bryce L Nordgren<BR><B>Sent:</B> Monday, November 21, 2011 5:07
PM<BR><B>To:</B> PostGIS Development Discussion<BR><B>Subject:</B>
[postgis-devel] ST_Union specification questions<BR></FONT><BR></DIV>
<DIV></DIV>So....<BR><BR>How are the p_, t_ and f_ expressions related? It
seems like these accumulate values in three different bands? If so, how was
the number "three bands" determined? If you don't specify one set of
expressions, does the corresponding band disappear out of the result? Or am I
reading it completely wrong: Does ST_Union always return a single band, and
the "state" expression is some sort of "scratch" band which is used to
accumulate information, but which is not actually returned?<BR><BR>Also,
aggregate functions really should not produce results which depend on the
order in which the individual records are encountered. Allowing this
functionality (see specifications: FIRST and LAST set of expressions) is
inviting trouble of a spurious and random nature, particularly when results
from Windows are compared with results from linux. The answer should always be
the same, just like the geometry version of ST_Union always returns the same
value. The solution may be to limit the functions which are allowed to appear
in the expression to other
aggregates...<BR><BR>Bryce<BR></BLOCKQUOTE></BODY></HTML>