def remove(src, rel, dst):
    """
    Returns an SQL statement that removes edges from
    the SQL backing store. Either `src` or `dst` may
    be specified, even both.

    :param src: The source node.
    :param rel: The relation.
    :param dst: The destination node.
    """
    smt = 'DELETE FROM %s' % rel
    queries = []
    params = []

    if src is not None:
        queries.append('src = ?')
        params.append(src)

    if dst is not None:
        queries.append('dst = ?')
        params.append(dst)

    if not queries:
        return smt, params
    smt = '%s WHERE %s' % (smt, ' AND '.join(queries))
    return smt, params