How to increase the value of a field by one?

[kerim]

I am writing a script to keep track of downloads, and I am having lots of difficulty writing the code to increase the field "num" (for number of downloads) by one each time there is a download.

Right now I have the script:

$num++

$sql = mysql_query (UPDATE $table WHERE id='$id' SET num='$num');

But it insists on updating every row in the table, not just the row I want to update!!! If I try anything else, I either get a syntax error, or no result at all . . .

Maybe if I saw some samples of how other people do this in their scripts I could figure it out.

Thanks!

kerim

[freakysid]

Firstly you have the structure of your sql statement mixed up a little and this is why it is not performing as you wish. The sql you provided should be written like:

UPDATE $table SET num='$num' WHERE id='$id'

However, there is a simpler way of incrementing the value of a field in the database:

UPDATE $table SET num = num + 1 WHERE id='$id'

[kerim]

Thanks. I tested the syntax right in MySQL manager and it works fine, but for some reason it is not working in the script. Below is th e whole script, do you see anything obviously wrong? Thanks.

kerim

<?PHP

// This script is an adaptation of Download Manger
// which can be seen at (www.tunga.com/PHP)

include("downlogin.php");

$filelist = mysql_query(
"SELECT * FROM files WHERE id='$id'");

while ($row = mysql_fetch_array($filelist)) {
$id = $row["id"];
$filename = $row["filename"];
$num = $row["num"];

// add 1 to number of downloads

$sql = mysql_query("UPDATE files SET num = num + 1 WHERE id='$id' or*DIE(mysql_error())");

// sends them the PDF file

$file_location = "****deleted for security****";


$file_path = $file_location . $filename;
if (detect_browser($HTTP_USER_AGENT) == "ie")
{
Header("Content-type: application/force-download");
}else{
Header("Content-Type: application/octet-stream");
}
Header("Content-Length: ".filesize($file_path));
Header("Content-Disposition: attachment; filename=$filename");
readfile($file_path);
}
// this is the function called to determine the browser

function detect_browser($variable)
{
if(eregi("(msie) ([0-9]{1,2}.[0-9]{1,3})", $variable))
{
$content = "ie";
}else{
$content = "nn";
}
return $content;
}


?>

[Chris Roane]

Try this:

$sql = mysql_query("UPDATE files SET num = '$num + 1' WHERE id='$id' or DIE(mysql_error())");

Technically, it shouldn't make a difference, but you never know.

[kerim]

Thanks. I tried the different syntax. I even found another syntax error (one of the spaces was not a real space character), but no luck. It still is not updating the database. Like I said, the file downloads fine, although annoyingly the acrobat 5 plugin manages to grab the file before download and so it appears in the browser. When this happens, it also avoids naming the file correctly - giving it the name of the PHP script instead. This is a real bummer, since this script was written partically to avoid that problem by pulling the filename from the SQL database.

kerim

[freakysid]

$sql = mysql_query("UPDATE files SET num = num + 1 WHERE id='$id' or*DIE(mysql_error())");

should be

$sql = mysql_query("UPDATE files SET num = num + 1 WHERE id='$id'") or*DIE(mysql_error());

[kerim]

Thank you all so much for helping a poor novice coder who has no idea! I've been working on this script for *months* and it finally works! (Except for the Acrobat issue I mentioned.) Maybe someday there will be a tool for the MacOS that actually checks my syntax for me!

Cheers.

kerim