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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_from(self, query):
 """ Compile the "from" clause for an update with a join. :param query: A QueryBuilder instance :type query: QueryBuilder :return: The compiled sql :rtype: str """

        if not query.joins:
            return ""

        froms = []

        for join in query.joins:
            froms.append(self.wrap_table(join.table))

        if len(froms):
            return " FROM %s" % ", ".join(froms)

        return ""