issue with mysql_num_rows

[pkghost]

This is the error I'm getting:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/pkghost/public_html/php/users/register.php on line 26

I'm doing a user login tutorial, and i run into trouble when i try to query the database and see if the username and email address that the user is attempting to register already exist. this is the code

if($password == $confirm){ //if the password fields match, check their email address against the database
$mailQ = "SELECT * FROM users WHERE email=$email, $db";
$result = mysql_query($mailQ);
$num_mails = mysql_num_rows($result);

if($num_mails == 0){ //if there are no entries for the query, then check the username...

//more code

So the mysql_num_rows($result) is where I'm having trouble. I don't know why its not working, ive fiddled here and there and it won't cooperate. Also, is there a better way to check if an entry already exists in teh database other than SELECT and checking the number of rows in the selection? thanks

[planetsim]

You may want to check your Query normally when you get an error like this its normally because the Query didnt execute correctly and gives a false value into the variables your using. So always check the Query

if($password == $confirm){ //if the password fields match, check their email address against the database
$mailQ = "SELECT * FROM users WHERE email=$email, $db";
$result = @mysql_query($mailQ)or die("MySQL Query Error: your error here");

/*
you could do it like this as well

if (!($result=@mysql_query($mailQ)))
{
  die("MySQL Error: your error");
}
*/
$num_mails = mysql_num_rows($result); 

[edit]
You will notice that this error is because of the

"SELECT * FROM users WHERE email=$email, $db";

$db is not in a proper SQL format. you may want to do it like so

mysql_query($mailQ,$db);
[/edit]

[Frederick]

A tip once you located the resource error, use the following example to shorten your code.

$mailQ = "SELECT * FROM users WHERE email = '$email' ";
$result = mysql_query($mailQ) or die (mysql_error());
if (!mysql_num_rows($result)) {
    // echo your failure message
} else {
    // continue here
}

[planetsim]

Ill just comment on what you showed Frederick.

Firstly you really shouldnt throw a mysql_error() unless its on a testing server.

Secondly mysql_num_rows is relatively useless in the if statement it really should be given a result then checked otherwise if you were to check how many rows you would need to do another mysql_num_rows if it returned true.

[pkghost]

planetsim:

this time im not getting any compile errors, but i do get a ' RegisterMySQL Query Error' where 'MySQL Query Error' is the error message in the following code:

if($password == $confirm){
$mailQ = "SELECT * FROM users WHERE email=$email";
$result = @($mailQ) or die("MySQL Query Error");
$num_mails = mysql_num_rows($result);

Also, I'm curious about the @symbol in front of mysql_query.. what does it do? and the $db variable i threw in just to see if it wasn't selecting the right database, ive never used it in the past with only one database connection. thanks for the help so far

[pkghost]

i got it all worked out! thanks for the help guys

[planetsim]

The @ symbol supresses errors so you can have your own, its a good way to go about creating custom errors, also very handy with MySQL functions as they sometimes display the errors to the user.

[pkghost]

so i've just read in your sticky newbie tute... too bad i didnt read it first. keep up the good work planetsim!