'Returns the SELECT SQL string for the given field.  Figures out
if any custom selection SQL is needed for the column  The `alias`
keyword may be used to manually specify the database table where
the column exists, if not in the model associated with this
`GeoQuery`.  Similarly, `column` may be used to specify the exact
column name, rather than using the `column` attribute on `field`.'

def get_field_select(self, field, alias=None, column=None):

    sel_fmt = self.get_select_format(field)
    if (field in self.query.custom_select):
        field_sel = (sel_fmt % self.query.custom_select[field])
    else:
        field_sel = (sel_fmt % self._field_column(field, alias, column))
    return field_sel
