Improved code style of Query.table_alias() usage.

                result.append('%s%s%s' % (connector, qn(name), alias_str))

            first = False

        for t in self.query.extra_tables:

            alias, unused = self.query.table_alias(t)

            alias, _ = self.query.table_alias(t)

            # Only add the alias if it's not already present (the table_alias()

            # calls increments the refcount, so an alias refcount of one means

            # this is the only reference.

        If 'create' is true, a new alias is always created. Otherwise, the

        most recently created alias for the table (if one exists) is reused.

        """

        current = self.table_map.get(table_name)

        if not create and current:

            alias = current[0]

        alias_list = self.table_map.get(table_name)

        if not create and alias_list:

            alias = alias_list[0]

            self.alias_refcount[alias] += 1

            return alias, False

        # Create a new alias for this table.

        if current:

        if alias_list:

            alias = '%s%d' % (self.alias_prefix, len(self.alias_map) + 1)

            current.append(alias)

            alias_list.append(alias)

        else:

            # The first occurrence of a table uses the table name directly.

            alias = table_name

            return alias

        # No reuse is possible, so we need a new alias.

        alias, _ = self.table_alias(table, True)

        alias, _ = self.table_alias(table, create=True)

        if not lhs:

            # Not all tables need to be joined to anything. No join type

            # means the later columns are ignored.