def METHOD_NAME():
    bind = op.get_bind()
    session = db.Session(bind=bind)
    for chart in session.query(Slice):
        params = json.loads(chart.params or "{}")
        if "time_compare" in params or "comparison_type" in params:
            params.pop("time_compare", None)
            params.pop("comparison_type", None)
            chart.params = json.dumps(params, sort_keys=True)
    session.commit()
    session.close()