Using functions with EXPRESSION

[Stephen Woodbridge]

Sergey Miltchakov wrote:
> Hello! 
> 
> I have a 'mydate' and 'the_geom' fields in my table and want to color the
> shapes on my layer depending on the year of the 'mydate' value. What
> expression do I use in order to do that? Is it possible to use postgre
> 'date_part' function at all?
> 
> I tried several ways but none helped me. It just returns blank image
> (without the layer). Other expressions work fine.

Hi Sergey,

You might want to post your mapfile so we can help with that.

In general, I have been doing thematic mapping with postGIS and I 
usually try to classify the data in SQL and return back a normalized 
theme value between 1 and N, then I make my LAYER like:

LAYER
   CONNECTIONTYPE postgis
   CONNECTION "...."
   DATA "the_geom from (select the_geom, (<classification expression>) 
as theme from data_table where <blah blah blah>) as foo using unique gid 
using srid 4326"
   CLASSEXPRESSION theme
   CLASS
     EXPRESSION 1
     ....
   END
   CLASS
     EXPRESSION 2
     ...
   END
   ...
   CLASS
     # no EXPRESSION is default catch all
     ...
   END
END

YMMV,
   -Steve W.