list of unique values in a shapefile using an attribute query

[John B. Churchill]

The documentation for PHP/Mapscript shows that it is possible to query 
by attributes using "queryByAttributes" but I must supply the qstring to 
get a match.  Does anyone know of a way to get a list of unique values 
for a given field ?

What I want to do is populate a "select" control (aka combo box) on a 
form with the unique values from a field in a shapefile.  I'm 
essentially building a query form for attribute data that is stored in 
shapefiles.

It seems like this shouldn't be too difficult but I'm coming into this 
with a GIS background and am relatively new to php and mapserver.  Any 
help will be appreciated.

J.B.
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John B. Churchill, M.S.			http://alx.al.umces.edu/~jchurch/
GIS Specialist				(301) 689-7109

University of Maryland Center for Environmental Science
Appalachian Laboratory			http://www.al.umces.edu/
Environmental Science Education		http://alese.al.umces.edu/

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