'Helper function that returns the database column for the given field.
The table and column are returned (quoted) in the proper format, e.g.,
`"geoapp_city"."point"`.  If `table_alias` is not specified, the
database table associated with the model of this `GeoQuery` will be
used.  If `column` is specified, it will be used instead of the value
in `field.column`.'

def _field_column(self, field, table_alias=None, column=None):

    if (table_alias is None):
        table_alias = self.query.model._meta.db_table
    return ('%s.%s' % (self.quote_name_unless_alias(table_alias), self.connection.ops.quote_name((column or field.column))))
