What's wrong with this code?

Python

I get an error with this bit of code but I cant see anything wrong with it:

[PHP]$regnum = "SELECT * FROM $dbprefix.`users`";
$regnum2 = mysql_query($regnum);
$regnum3 = mysql_num_rows($regnum2);
$regtotal = $regnum3;[/PHP]

It just counts the number of users in a database... ive tried changing the prefix so its not using a variable, ive tried rearranging it...

This is probably a very simple mistake that Im just not picking up on...

The error is a mysql error:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home2/pythonsb/public_html/forum/index.php on line 19

Any ideas?
thanks

martian2k4

Normally with a error like that its because it aint managing to execute the first query so you got sommat wrong with the first query i am guessing $db_prefix.

martian2k4

i aint sure but maybe

$regnum = "SELECT * FROM `$dbprefix.users`";
$regnum2 = mysql_query($regnum);
$regnum3 = mysql_num_rows($regnum2);
$regtotal = $regnum3;

Python

no the line which is causing the problem is $regnum3 = mysql_num_rows($regnum2);

What i dont understand is that taht exact piece of code i had working in a different file... perhaps ill try changing some of the db stuff...it shouldnt make a difference tho

martian2k4

Ye i know it is the mysql_num_rows causing the problem but if the first querty dont work then mysql_num_rows wont b able to either

Python

lol. yeah i know... but what im saying is if the first query didnt work then there would be an error about that line too

Chroder

Not necessarily. An error with your SQL would not generate a PHP error, it would simply return false. Try adding some error printing to your code.

[php]$regnum2 = mysql_query($regnum) or die(mysql_error());[/php]

Also, you should always check the validity of a mysql result before using it for anything. In this case, the 'or die' will stop the script on a query error, but often times you don't want such intrusive error messages popping up. So it's best to test the result (mysql_query will return false on error) before using it in other functions like mysql_num_rows.

martian2k4

Yes thats what i was gonna say next