postgis_datasource_tokens_query.xml

<?xml version="1.0" encoding="utf-8"?>
<Map srs="+init=epsg:3857">
  <Layer name="field_shapes" status="on" srs="+init=epsg:4326">
    <Datasource>
      <Parameter name="type">postgis</Parameter>
      <Parameter name="host">localhost</Parameter>
      <Parameter name="dbname">node-mapnik-tmp-postgis-test-db</Parameter>
      <Parameter name="srid">4326</Parameter>
      <Parameter name="geometry_field">geom</Parameter>
      <Parameter name="table">
  (SELECT gid, geom FROM test WHERE gid = @fieldid) as field_shapes
      </Parameter>
      <Parameter name="estimate_extent">false</Parameter>
      <Parameter name="extent">-150,-85,150,85</Parameter>
    </Datasource>
  </Layer>
</Map>