presto-main/src/main/java/io/prestosql/operator/scalar/DateTimeFunctions.java/DateTimeFunctions/toUnixTime
class DateTimeFunctions:    @ScalarFunction("to_unixtime")
    @SqlType(StandardTypes.DOUBLE)
    public static double toUnixTime(@SqlType(StandardTypes.TIMESTAMP) long timestamp)
    {
        return timestamp / 1000.0;
    }