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refresh client webpage when data changes on server (php or javascript)

I want to present data (which is on the server) on the client (mobilphone). Data is changed rarely (once a day) or frequently (more times in a hour). I dont want to client always asks server because battery of mobil would drain fast. But I want to see the changed data as soon as possible on the phone. Is there any way to do this?
I could use php on the server or php/js on the client. The data is a file and its modified time can be read by server.

As far as I see you have two option that doesn't require the client to keep checking your server (not as much).
Web push
Web socket
I suggest use web-socket, which is more practical and with better cross-browser support.

Client access vs broadcast data from web server

I'm looking for technique or skils to fix the ways for new web site.
This site show the read time data which located on server as file or data on memory.
I'll use Node.js for server-side. But I can't fix how to get the data and show that to web site user.
Because this data have to update per 1 second at least.
I think it is similar to the stock price page.
I know there are a lot of ways to access data like AJAX, Angular.js, Socket.io..
Also each has pros and cons.
Which platform or framework is good in this situation?

This ultimately depends on how much control you have over the server side. For data that needs to be refreshed every second, doing the polling on client side would place quite the load on the browser.
For instance, you could do it by simply using one of the many available frameworks to make http requests inside some form of interval. The downsides to this approach include:
the interval needs to be run in the background all the time while the user is on the page
the http request needs to be made for every interval to check if the data has changed
comparison of data also needs to be performed by the browser, which can be quite heavy at 1 sec intervals
If you have some server control, it would be advisable to poll the data source on the server, i.e. using a proxying microservice, and use the server to perform change checking and only send data to clients when it has changed.
You could use Websockets to communicate those changes via a "push" style message instead of making the client browser do the heavy lifting. The flow would go something like:
server starts polling when a new client starts listening on its socket
server makes http requests for each polling interval, runs comparison for each result
when result has changed, server broadcasts a socket message to all connected clients with new data
The main advantage to this is that all the client needs to do is "connect and listen". This even works with data sources you don't control – the server you provide can perform any data manipulation needed before it sends a message to the client, the source just needs to provide data when requested.
EDIT: just published a small library that accomplishes this goal: Mighty Polling ⚡️ Socket Server. Still young, examine for your use if using.

If i used setInterval to request data from database, May it damage the server?

I'm trying to develop chat system in php, sql and ajax. I created function by ajax to get messages from database this function its event when window upload, so if i open 2 windows in browser to test the application, I found the messages bu when i send message it appear in just the window which send from not both of the 2 windows. To solve this problem i used setInterval function every 1 second to show messages.
Do this huge requests damage the server ??

I don't quite know what you meant with "Damage", but nothing can be really damaged by a few extra requests.
If you're wondering whether the webserver can handle the load, it really depends on how many chat sessions are going at the same time. Any decent web server should be able to handle a lot more than two requests per second. If you have thousands of chat sessions open, or you have very CPU intensive code, then you may notice issues.
A bigger issue may be your network latency. If your network takes more than a second for a round-trip communication with the server, then you may end up with multiple requests coming from the same client at the same time.

Which is more efficient to send WebSocket updates with a MySQL database change

I'm currently experimenting with WebSockets in a bid to reduce / remove the need for constant AJAX requests in a potentially low bandwidth environment. All devices are WebSocket compliant so there's no issue there, and I'm trying to keep it to native PHP WebSockets, no node.js or other frameworks / libraries (Which so far has been fine).
What I'm looking to do is to decide how to go about notifying connected clients about an update to a database by another Client. The use case in question is a person pressing a button on their device, which then alerts that persons manager(s) to that press. So the two options I have though of are as follows:
1. Looping a Database Query (PHP)
My first thought was to insert a query into the WebSocket server that is effectively saying "Has the alert field changed? If so, notify the manager(s)". Whilst this is the most straightforward and sensible approach (That I can think of), it seems wasteful to have a PHP script designed to reduce strain on the server, that is now running a query every second, however, at least this would ensure that when a Database update is detected, the update is sent.
2. Sending a notification from the Client
Another thought I had, was that when the client updates the Database, they could in fact send a WebSocket notification themself. This has the advantage of reducing any intensive and looped queries, but also means that I'd need to have a WebSocket message being sent every time I want to change any data, such as:
$.post("AttemptDatabaseUpdate.php", {Data}).function(Result) // Don't worry about the semantics of this, it's not actual code
{
if(Result == "Successful")
{
SendWebSocketNotification(OtherData);
}
}
Maybe this is the best option, as it is the most efficient, but I worry that there is a chance the connection may drop between updating the Database, and sending the WebSocket notification, which may create a need for a fallback check in the PHP file, much like the one in the first solution, albeit at a longer interval (Say every 30 seconds).
3. MySQL Trigger?
This is purely a guess, but perhaps another option is to create a MySQL trigger, which can somehow notify the server.php file directly? I've no idea how this would work, and would hazard a guess that this may end up with the same or similar Query requirements as solution #1, but it's just a though...
Thank you in advance for your help :)
EDIT: Solution possibility 4
Another thought has just popped into my head in fact, whereby the PHP file used to update the database could in fact have a WebSocket message built into it. So that when the PHP file updates the database, the WebSocket server is notified via PHP, is this possible?

If you use websockets, you should use notifications from client. That's one of their main use cases.
If you're worried about inconsistencies due to connection dropping or something changing in-between, you could implement a system similar to HTTP ETags, where client would send a hash code that you can respond on server side if there is a conflict in updating.
Update: I guess I understood your initial issue a bit wrong. If I understand your use case correctly: you are sending database updates from a client and after that all connected clients need to be updated. In that case, I think server should send the update messages after DB updates have been done, so I agree with solution 4. I am assuming here that your websocket server is the same server running PHP and doing the DB updates.
However, depending on your use case, client should still send a hash value on the next request identifying its "view of the world", so you would not be doing identical updates multiple times if a connection gets broken.
Update 2: so it was now understood that you indeed use a separate, standalone websocket server. Basically you have two different web servers on the server side and are having an issue on how to communicate between the two. This is a real issue, and I'd recommend only using one server at a time - either take a look at using Apache websocket support (experimental and not really recommended) or migrating your php scripts to the websocket instance.
Neither PHP or Apache was really build with websockets in mind. It is quite easy to set up a standalone websocket server using only PHP, but it might not be so easy then to migrate the rest of the PHP stack to it if the code is relying on Apache/web server on. Apache websocket support also is hardly optimal. For a real websocket solution, unfortunately, best practice would be using a technology that is built for it from the ground up.

The better answer is to send notification through Server side when database is updated by PHP script, so that script have to add options of web sockets to directly send notification to all web socket clients registered.
User send content->Php script process content and save data according to true condition->check database is updated by checking return of mysql_query/other alternative->if true than use web-socket and send notification to all users
now this is more easy/handy/bandwidth saver.

'Web' based push notifications for internal-only application

I'm already tossing around a solution but as I haven't done something like this before I wanted to check what SO thought before implementation.
Basically I need to modify an existing web based application that has approximately 20 users to add push notifications. It is important that the users get the notifications at the same time (PC-A shouldn't get an alert 20 seconds before PC-B). Currently the system works off of AJAX requests, sending to the server every 20 seconds and requesting any updates and completely rebuilding the table of data each time (even if data hasn't changed). This seems really sloppy so there's two methods I've come up with.
Don't break the connection from server-client. This idea I'm tossing around involves keeping the connection between server and client active the entire time. Bandwidth isn't really an issue with any solution as this is in an internal network for only approximately 20 people. With this solution the server could push Javascript to the client whenever there's an update and modify the table of data accordingly. Again, it's very important that every connected PC receives the updates as close to the same time as possible. The main drawback to this is my experience, I've never done it before so I'm not sure how well it'd work or if it's just generally a bad idea.
Continue with the AJAX request, but only respond in intervals. A second solution I've thought of would be to allow the clients to make AJAX requests as per usual (currently every 20 seconds) but have the server only respond in 30 second intervals (eg 2:00:00 and 2:00:30 regardless of how many AJAX requests it recieves in that span of time). This would require adjusting the timeout for the AJAX request to prevent the request timing out, but it sounds okay in theory, at least to me.
This is for an internal network only, so bandwidth isn't the primary concern, more so that the notification is received as close to each other as possible. I'm open to other ideas, those are just the two that I have thought of so far.
Edit
Primarily looking for pros and cons of each approach. DashK has another interesting approach but I'm wondering if anyone has experience with any of these methods and can attest to the strengths and weaknesses of each approach, or possibly another method.

If I understand well your needs I think you should take a look to Comet
Comet is a web application model in which a long-held HTTP request allows a web server to push data to a browser, without the browser explicitly requesting it. Comet is an umbrella term, encompassing multiple techniques for achieving this interaction. All these methods rely on features included by default in browsers, such as JavaScript, rather than on non-default plugins.
The Comet approach differs from the original model of the web, in which a browser requests a complete web page at a time.

How about using an XMPP server to solve the problem?
Originally designed to be an Instant Messaging platform, XMPP is a messaging protocol that enables users in the system to exchange messages. (There's more to this - But let's keep it simple.)
Let's simplify the scenario a little bit. Imagine the following:
You're a system admin. When the system
has a problem, you need to let all the
employees, about 20 of them, know that
the system is down.
In the old days, every employee will
ask you, "Is the system up?" every
hour or so, and you'll response
passively. While this works, you are
overloaded - Not by fixing system
outage, but by 20 people asking for
system status every hour.
Now, AIM is invented! Since every
employee has access to AIM, you
thought, "Hey, how about having every
single one of them join a 'System
Status' chat room, and I'll just send
a message to the room when the system
is down (or is back)?" By doing so,
employees who are interested in
knowing system status will simply join
the 'System Status' room, and will be
notified of system status update.
Back to the problem we're trying to solve...
System admin = "System" who wants to notify the web app users.
Employees = Web app users who wants to receive notification.
System Status chat room = Still, system Status chat room
When web app user signs on to your web app, make the page automatically logs them onto the XMPP server, and join the system status chat room.
When system wants to notify the user, write code to logon to the XMPP server, join the chat room, and broadcast a message to the room.
By using XMPP, you don't have to worry about:
Setting up "Lasting connection" - Some open source XMPP server, eJabberd/OpenFire, has built-in support for BOSH, XMPP's implementation of the Comet model.
How the message is delivered
You however will need the following:
Find a Javascript library that can help you to logon to an XMPP server. (Just Google. There're a lot.)
Find a XMPP library for the server-side code. (XMPP library exists for both Java & C#. But I'm not sure what system you're using behind the scene.)
Manually provision each user on the XMPP server (Seems like you only have 20 people. That should be easy - However, if the group grows bigger, you may want to perform auto-provisioning - Which is achievable through client-side Javascript XMPP library.)
As far as long-lasting AJAX calls, this implementation is limited by the at-most-2-connection-to-the-same-domain issue. If you used up one connection for this XMPP call, you only have 1 more connection to perform other AJAX calls in the web-app. Depending on how complex your webapp is, this may or may not be desirable, since if 2 AJAX calls have already been made, any subsequent AJAX call will have to wait until one of the AJAX pipeline freed up, which may cause "slowness" on your app.
You can fix this by converting all AJAX calls into XMPP messages, and have a bot-like user on the server to listen to those messages, and response to it by, say, sending back HTML snippets/JSON objects with the data. This however might be too much for what you're trying to achieve.
Ahh. Hope this makes sense... or not. :p

See http://ajaxpatterns.org/HTTP_Streaming
It allows You to push data from the server when server wants it. Not just after the query.
You could use this technique without making large changes to the current application, and synchronize output by the time on the server.

In addition to the other two great options above, you could look at Web Workers if you know they have latest Chrome, Safari, FF, or Opera for a browser.
A Worker has the added benefit of not operating in the same thread as the rest of the page, so performance will be better. The downside is that, for security purposes, you can only send string data between the two scripts and the worker does not have window or document context. However, JSON can be represented as a string, so there's really no limit to the data.
Workers can receive data multiple times and asynchronously. You set the onmessage handler to act each time it receives something.

If you can ask every user to use a specific browser (Latest Safari or Chrome), you can try WebSockets too.