presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/currentTimeZone
class DateTimeFunctions:    @Description("current time zone")
    @ScalarFunction("current_timezone")
    @SqlType(StandardTypes.VARCHAR)
    public static Slice currentTimeZone(ConnectorSession session)
    {
        return utf8Slice(session.getTimeZoneKey().getId());
    }