Mysql PHP Arbitrary Increment

Question

I'm trying to increment +1 impression every time an ad is displayed on my site, however the variable increments +2 to +3 arbitrarily. I've removed everything that's working correctly and I made a page with only this code in it:

<?php
require "connect_to_mydb.php";
echo 'Hello***** '.$testVariable=$testVariable+1;
mysql_query("UPDATE `imageAds` SET `test`=`test`+1 WHERE `id`='1'");
?>

Every time the page is refreshed the, test increments arbitrarily either +2 or +3 and my page displays Hello***** 1 (Just to show its not looping). Access is restricted to this page so it's not other users refreshing the page.

Also, id and test are int(11) in the DB.

My DB required connection has nothing in it that would interfere.

Edit

Here is an updated code:

<?php
require "connect_to_mydb.php";
mysql_query("UPDATE `imageAds` SET `test`=`test`+1 WHERE `id`='1'");
$sql = mysql_query("SELECT * FROM imageAds WHERE id='1' LIMIT 1");
$check = mysql_num_rows($sql);
if($check > 0){ 
    $row = mysql_fetch_array($sql);
    echo $row['test'];
}
?>

Increments by +2 everytime

Edit This is whats in connect_to_mydb.php

<?php  
$db_host = "*************************"; 

$db_username = "*********";  

$db_pass = "**********";  

$db_name = "**************";

mysql_connect("$db_host","$db_username","$db_pass") or die ("could not connect to   mysql");
mysql_select_db("$db_name") or die ("no database");              
?>

Your test code doesn't display the value of test, so how do you know how much it's incrementing by? — Oliver Charlesworth
– Oliver Charlesworth, Commented Apr 29, 2012 at 20:31
Can you check that when you refresh the page only 1 http request is being sent. — alexarno
– alexarno, Commented Apr 29, 2012 at 20:35
You should modify your PHP code to SELECT and echo the value of test before and after the UPDATE. — Oliver Charlesworth
– Oliver Charlesworth, Commented Apr 29, 2012 at 20:35
Please post the code for connect_to_mydb.php. You can replace the security sensitive information with ***** if you wish. — Mark Byers
– Mark Byers, Commented Apr 29, 2012 at 20:42

Mark Byers · Accepted Answer · 2012-04-29 20:37:51Z

3

Either there's a bug in MySQL's implementation of UPDATE, or you're doing something wrong in some code you haven't posted.

Hint: It's very unlikely to be a bug in MySQL. Other people would have noticed it.

From what you've shown, it looks like your page is being loaded multiple times.

This attempt to prove that the code is only being called once doesn't prove anything:

echo 'Hello***** '.$testVariable=$testVariable+1;

This will always print the same thing (Hello***** 1) even if you open this page multiple times because the value of $testVariable is not preserved across seperate requests.

edited Apr 29, 2012 at 20:37

answered Apr 29, 2012 at 20:32

Mark Byers

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1 Comment

vimdude Over a year ago

It depends what require "connect_to_mydb.php"; is doing. It might have $testVariable defined global.

phpKid · Accepted Answer · 2012-04-30 05:17:28Z

This +2/+3 error is occurring only with Chrome and my Mobile Android browser and the code is solid. I looked to see if there is any issue with Chrome sending more than one http request (thx user1058351) and there is which is documented here:

http://code.google.com/p/chromium/issues/detail?id=39402

So since this way was unreliable I just completed a work around that is solid. Instead of including a PHP file that updates the amount of ad impressions on reload, I now have it so when the page loads, an AJAX request is sent to a separate PHP file which updates the ad stats and returns the appropriate data. The key I think is to send it through the JS code so only one http request can be sent to increment the data.

Thank you to all who responded especially user1058351 and Mark Byers (not a bug in MYSQL but possibly appears to be a bug in Chrome).

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