mysql_num_rows() error

mattisrad

i installed this private messaging system on my login script from here http://www.pixel2life.com/publish/tutorials/608/simple_private_messaging_system/. thing is i get this error
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/vol11/xtreemhost.com/xth_4280991/htdocs/pm.php on line 137. how do i fix this?

mattisrad

this is the login script i use btw http://evolt.org/PHP-Login-System-with-Admin-Features?from=1550&comments_per_page=50

NogDog

That sort of error usually indicates that the query had a SQL syntax error which prevented it from running, so the mysql_query() call returned a boolean false instead of a query result resource. Or your database connection may have failed, which then caused mysql_query() to fail.

Adding the following to the start of the script may help you locate the source of the problem:

<?php
ini_set('display_errors', 1); // set to 0 for production version
error_reporting(E_ALL);
// rest of script.....
?>

johanafm

Replace $result with whatever variable you use as paramter in the function call on 137 and
preceed that line with

if ($result === false)
	error_log(mysql_errno . ': ' .mysql_error());

mattisrad

nothing comes up. isnt there an alternative to mysql_num_rows? how would i edit the script?

NogDog

It's not an issue of mysql_num_rows() not working, it's an issue of the mysql_query() which preceded it not working, and the resulting return value then being used as the parameter to mysql_num_rows(). So you need to find out why it (the mysql_query() call) is returning false instead of a valid resource. Try johanafm's code, but change the error_log(mysql_error()) to die(mysql_error()) (and make sure display_errors is turned on as I indicated above).

johanafm

As for your concern with mysql_num_rows, that function is not your problem. As NogDog wrote in his first post, the problem is that you call it like this

// the result of the query is false, not a result set resource
$result = mysql_query($some_query);
// which means the above is the exact same thing as
$result = false;

// and since the above is false...
mysql_num_rows($result);
// the above line is the same as
mysql_num_rows(false);

mattisrad

johanafm;10930600 wrote:
Replace $result with whatever variable you use as paramter in the function call on 137 and
preceed that line with
if ($result === false)
	error_log(mysql_errno . ': ' .mysql_error());

just to make sure i'm not doing it wrong can you explain more on this?

johanafm

First off, there's an error there. It's supposed to be mysql_errno() since it's a function call. Both functions uses the latest created db link unless a link is explicitly specified like this

$link = mysql_connect( /* ... */);
$result = mysql_query("Will not work");
echo mysql_errno($link);

mysql_errno() shows an error number and mysql_error() shows an error message.

$result = mysql_query("Something that goes wrong");

/* $result is now false, so it can't be used with functions that take a result set resource, such as
    mysql_num_rows or mysql_fetch_assoc
    If it is indeed a result set resource, then the if check below evaluates to false and is bypassed
*/
if (!$result) {
// my suggestion, which invokes the current error_handler (may display, mail, write to file)
	error_log(mysql_errno() . ': ' . mysql_error());
// or NogDog's suggestion, which write to standard output and terminates the script
	die(mysql_errno() . ': ' . mysql_error());
}

/* With my approach, you'd somehow need to deal with not proceeding to use $result with
    mysql functions, since they will fail. e.g */
else {
	// mysql_functions here
}

You should follow a similar approach when conneting to the db as well

$link = mysql_connect( /* ... */);
if (!$link) {
	// decide what to do...
}