Compile the additional where clauses for updates with joins.

        :param query: A QueryBuilder instance
        :type query: QueryBuilder

        :return: The compiled sql
        :rtype: str

def _compile_update_wheres(self, query):
        """
        Compile the additional where clauses for updates with joins.

        :param query: A QueryBuilder instance
        :type query: QueryBuilder

        :return: The compiled sql
        :rtype: str
        """
        base_where = self._compile_wheres(query)

        if not query.joins:
            return base_where

        join_where = self._compile_update_join_wheres(query)

        if not base_where.strip():
            return "WHERE %s" % self._remove_leading_boolean(join_where)

        return "%s %s" % (base_where, join_where)