def get_default_columns(self, with_aliases=False, col_aliases=None,
            start_alias=None, opts=None, as_pairs=False, from_parent=None):
        result = []
        if opts is None:
            opts = self.query.get_meta()
        qn = self.quote_name_unless_alias
        qn2 = self.connection.ops.quote_name
        aliases = set()
        only_load = self.deferred_to_columns()
        if not start_alias:
            start_alias = self.query.get_initial_alias()
        # The 'seen_models' is used to optimize checking the needed parent
        # alias for a given field. This also includes None -> start_alias to
        # be used by local fields.
        seen_models = {None: start_alias}

        for field, model in opts.get_concrete_fields_with_model():
            if from_parent and model is not None and issubclass(from_parent, model):
                # Avoid loading data for already loaded parents.
                continue
            alias = self.query.join_parent_model(opts, model, start_alias,
                                                 seen_models)
            table = self.query.alias_map[alias].table_name
            if table in only_load and field.column not in only_load[table]:
                continue
            if as_pairs:
                result.append((alias, field))
                aliases.add(alias)
                continue
            if with_aliases and field.column in col_aliases:
                c_alias = 'Col%d' % len(col_aliases)
                result.append('%s.%s AS %s' % (qn(alias),
                    qn2(field.column), c_alias))
                col_aliases.add(c_alias)
                aliases.add(c_alias)
            else:
                r = '%s.%s' % (qn(alias), qn2(field.column))
                result.append(r)
                aliases.add(r)
                if with_aliases:
                    col_aliases.add(field.column)
        return result, aliases
Checks time element to see if start or end time must be detected on the file system.
dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/Django-1.6.10/django/db/models/sql/compiler.py/SQLCompiler.get_default_columns--crossover with--dataset/ETHPy150Open nasa-gibs/onearth/src/layer_config/bin/oe_configure_layer.py/detect_time