How can Create OVF file (for OGR MYSQL connection) interactively

[Frank Warmerdam]

Bart van den Eijnden (OSGIS) wrote:
> David,
> 
> my guess without studying the code is that this does not make a 
> difference in performance.
> 
> I think a Mapserver EXPRESSION will make it into the SQL that OGR passes 
> to MySQL in the end. I don't believe Mapserver does the filtering itself 
> on the whole dataset.

Bart / David,

I believe that an EXPRESSION for an OGR connection that starts with the
keyword WHERE is passed down into OGR as an "attribute filter" on the
layer and so will be potentially evaluated in the database.  I'm not exactly
certainly if this will get properly passed through the VRT mechanism and onto
an ODBC datasource, which I think was the original question.  Some
experimentation with OGR debugging turned on for clues might be appropriate.

To turn on OGR debugging I think you can add the following in your .map file:

   CONFIG "CPL_DEBUG" "ON"

This should produce extra debug messages to the stderr which at least on unix
will end up in the apache error_log file.

Best regards,
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