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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _compile_update_join_wheres(self, query):
 """ Compile the "join" clauses for an update. :param query: A QueryBuilder instance :type query: QueryBuilder :return: The compiled sql :rtype: str """

        join_wheres = []

        for join in query.joins:
            for clause in join.clauses:
                join_wheres.append(self._compile_join_constraints(clause))

        return " ".join(join_wheres)