def _combine(**kw):
    """
    Combine two table dictionaries used in a join to produce a single dictionary
    that can be used in formatting.
    """
    result = {}
    for tableRole, tableDictionary in kw.items():
        result.update([("%s:%s" % (tableRole, k), v)
                       for k, v in tableDictionary.items()])
    return result