Counter does not increment in PHP/MySQL

Question

I need to create a counter for member section (count the number of times a user logged).

I have the following script (counter.php):

<?php
    $conn = mysql_connect("localhost", "myuser", "mypass");
    mysql_select_db("test");

    $sql = "SELECT views FROM members WHERE mid = " . $_GET['mid'];     
    $result = mysql_query($sql); 
    if (!$result)
        {
        mail(ADMIN, 'Cannot Get: ' . mysql_error(), mysql_error());  
        }
    while ($row = mysql_fetch_assoc($result)) 
        {
        $count = $row['views']++; 
        }
    $query = "UPDATE members SET views = '$count' WHERE mid = " . $_GET['mid']; 
    mysql_query($query); 
    mysql_close($conn);

    // show the logo using header() and readfile(); // that part work
?>

DB:

CREATE TABLE `members` (
  `mid` int(11) NOT NULL AUTO_INCREMENT,
  `views` int(11) DEFAULT '0',
  /* etc...*/
  PRIMARY KEY (`mid`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

Now, what I do in my .htaccess file is:

RewriteEngine On
RewriteRule ^img/logo([0-9]+).jpg$ /counter.php?mid=$1 [L]

but for some reason my counter does not count correctly. What am I missing?

Be sure to learn all about SQL injection and input filtering. — grossvogel
– grossvogel, Commented Oct 17, 2011 at 18:29
Indeed. Don't try to put the id mid=1;delete%20from%20members;-- in the url. :) — GolezTrol
– GolezTrol, Commented Oct 17, 2011 at 18:32
the rewrite rule is not providing any security at all, its just a url alias. Someone could just as easily hit up counter.php with the sql injection parameters — carpii
– carpii, Commented Oct 17, 2011 at 19:27

endyourif · Accepted Answer · 2011-10-17 18:31:40Z

12

You could probably just simplify it and do the following:

$query = "UPDATE members SET views = views + 1 WHERE mid = " . $_GET['mid']; 
mysql_query($query); 

if (mysql_affected_rows() == 0) {
   mail(ADMIN, 'Cannot Get: ' . mysql_error(), mysql_error());
}

mysql_close($conn);

No need to do initial check.

answered Oct 17, 2011 at 18:31

endyourif

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3 Comments

grossvogel Over a year ago

+1 Not only is this more efficient than doing two queries, but database locking will help prevent multiple concurrent requests from being counted as 1.

GolezTrol Over a year ago

Smart thinking. Less risk on issues with simultaneous counts indeed.

Julius F Over a year ago

This is going to be hardly inefficient if you get a lot of visitors, since the database locks will block the system too heavy. Try to read more about sharded counters, used @ google's appengine

Peter · Accepted Answer · 2011-10-17 18:28:16Z

5

use this

$count = $row['views'] + 1;

or

$count = ++$row['views'];

or

$query = "UPDATE members SET views = views + 1 WHERE mid = " . $_GET['mid'];

syntax:

$x = 1;
$count = $x++;
// $count = 1

$x = 1;
$count = ++$x;
// $count = 2

answered Oct 17, 2011 at 18:28

Peter

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3 Comments

grossvogel Over a year ago

+1 I don't see what's wrong with this. Downvoter, care to enlighten us?

GolezTrol Over a year ago

Failed to address the actual cause of the problem at first. But it seems ok after he copied my answer. ;-) Although it still could do Undone my downvote, because at least the answer now addresses the problem, although it could do with a little more explanation.

grossvogel Over a year ago

@GolezTrol: I see. Your answer does have a better explanation of pre- and post-increment. I've upvoted you.

GolezTrol · Accepted Answer · 2011-10-17 18:28:22Z

2

The problem is in the line

$count = $row['views']++;

This actually says:
- Assign the value of view to $count
- Increment views.

But you want:

$count = ++$row['views'];

Which says:
- Increment views.
- Assign the (incremented) value of view to $count

A subtle difference. :~)

answered Oct 17, 2011 at 18:28

GolezTrol

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