How can I refresh a page when a database is updated?

This is how I recently implemented a solution using jQuery.

PHP increments a field in the database every time a significant update occurs.

<?php//  Call this function when data changesfunction update_clients(){    mysql_query( "UPDATE pageGen SET id = id + 1 LIMIT 1" );}//  Call this function to get the ID to pass to JavaScriptfunction get_update(){    $result = mysql_query( "SELECT id FROM pageGen LIMIT 1" );    $update = mysql_result( $result, 0, 'id' );    return $update;}?>

When the page is initially loaded, populate a JavaScript variable with a number from the database:

<script type="text/javascript">var pageGenID = 25218603  //  generated by PHPvar processUpdate = function( response ) {    if ( pageGenID < response )     {        replace_current_data_with_new_via_ajax();        pageGenID = response;    }}//  Compare our Page Generate ID against that of the servervar checkUpdates = function(){    serverPoll = setInterval( function()    {        $.get('script_to_return_latest_pageGenID.php',           { lastupdate: 1 },           processUpdate, 'html');    }, 10000 )};//  Check for updates every 10 seconds$( document ).ready( checkUpdates );</script>

Here is what I did and used the answer you marked but I think there is a few things to change there.In the main page ( that you want to refresh if something changed in the database).I created a table in my database called setting, in this table i created a row that called rowCounter.the rowCounter is being updated when the numbers of rows in the table you check has been changed.so my code split in two blocks. one that giving me the number from the setting > rowCounter and the second is the script that give me the current number in the table. if they are not equal then I refresh the page.

so this is the first file you need
script_to_return_latest_pageGenID.php

// here you will make you connection query.$result = mysql_query( "SELECT rowCounter FROM setting WHERE `id`='2'" );$update = mysql_fetch_assoc($result);        echo implode($update);    $count=mysql_query("SELECT `id` FROM log_".$datestamp."")or die(mysql_error);    $number =  mysql_num_rows($count);//echo $number;    $countFromSetting=mysql_query("SELECT `rowCounter` FROM setting  WHERE id='2'")or die(mysql_error);    $numberFromSetting=implode(mysql_fetch_assoc($countFromSetting));    if($number != $numberFromSetting)        {            mysql_query("UPDATE setting SET `rowCounter`='$number' WHERE `id`='2'")or die(mysql_error);        }

In the main page you will write the two blocks of code I provided and you should put it before the script.

$countFromSetting=mysql_query("SELECT `rowCounter` FROM setting  WHERE id='2'")or die(mysql_error);           $numberFromSetting=implode(mysql_fetch_assoc($countFromSetting));

After this code you put the script that will query every few seconds the php script, check if the numbers are not equal it will refresh the page.

var pageGenID = "<?php echo $numberFromSetting; ?>"; var processUpdate = function( response ) {var x=response;//console.log(pageGenID); by removing the remarks you will see the compared numbers all the time.//console.log(x);if ( pageGenID != x ) {    //replace_current_data_with_new_via_ajax();    pageGenID = response;    window.location.reload();          }} var checkUpdates = function(){    serverPoll = setInterval( function()  {$.get('script_to_return_latest_pageGenID.php',       { lastupdate: 1 },       processUpdate, 'html');  }, 5000 ) };    $( document ).ready( checkUpdates );

I believe you'd have to poll the database when you use PHP, PHP doesn't exist in a long running process as in the case of a Java container where the Java web application could create a persistent connection (in theory) you'll likely need to employ some sort of polling mechanism by which I mean setup a timer in Javascript or whatever your client code is to periodically make the request, in terms of increasing efficiency for this if need be you could create a flag on the users table and set the flag to indicate that the database has been invalidated since the user last polled, then your first check would be if invalidation has happened since that user last updated rather than sending everything to everyone all the time. Alternatively I think you'd need to abandon PHP for this task.