**Use case**

It is better than hostname in the following example:
```
SELECT hostname() AS host, event_time, round(value, 2) AS v, bar(v, 0, 10, 100) FROM system.asynchronous_metric_log WHERE event_date >= yesterday() AND event_time >= now() - 300 AND metric = 'LoadAverage1' ORDER BY host, event_time
```

Because hostnames can be non-informative like `ip-172-31-5-46`.

{
    public:
        static constexpr auto name = "hostName";
        static FunctionPtr create(ContextPtr context) { return std::make_shared<FunctionHostName>(context); }
        explicit FunctionHostName(ContextPtr context) : FunctionConstantBase(DNSResolver::instance().getHostName(), context->isDistributed()) {}
    };
    class FunctionServerUUID : public FunctionConstantBase<FunctionServerUUID, UUID, DataTypeUUID>
    {
    public:
        static constexpr auto name = "serverUUID";
        static FunctionPtr create(ContextPtr context) { return std::make_shared<FunctionServerUUID>(context); }
        explicit FunctionServerUUID(ContextPtr context) : FunctionConstantBase(ServerUUID::get(), context->isDistributed()) {}
    };
    class FunctionTcpPort : public FunctionConstantBase<FunctionTcpPort, UInt16, DataTypeUInt16>
    {
    public:
        static constexpr auto name = "tcpPort";
        static FunctionPtr create(ContextPtr context) { return std::make_shared<FunctionTcpPort>(context); }
        explicit FunctionTcpPort(ContextPtr context) : FunctionConstantBase(context->getTCPPort(), context->isDistributed()) {}
    };
    
    class FunctionTimezone : public FunctionConstantBase<FunctionTimezone, String, DataTypeString>
    {
    public:
        static constexpr auto name = "timezone";
        static FunctionPtr create(ContextPtr context) { return std::make_shared<FunctionTimezone>(context); }
        explicit FunctionTimezone(ContextPtr context) : FunctionConstantBase(String{DateLUT::instance().getTimeZone()}, context->isDistributed()) {}
    };
    
    class FunctionUptime : public FunctionConstantBase<FunctionUptime, UInt32, DataTypeUInt32>