put this
echo $query_username;
right after
$query_username = "SELECT id FROM users WHERE username = '$username'";
sounds like $username isn't coming thru, you may have to use
<?
$query_username = "SELECT id FROM users WHERE username = '" . $_POST['username'] . "'";
?>
It's coming through fine:
SELECT id FROM users WHERE username='testuser'
Query was empty
This has been annoying me for several hours now 
Interestingly, if I refresh the page, it works fine and I get printed before the HTML of the page:
SELECT id FROM users WHERE username='joely'
Resource id #2
from the PHP:
echo $query_username."<br>";
$doquery_username = mysql_query($query_username) or die(mysql_error());
echo $doquery_username."<br>";
$numrows_username = mysql_num_rows($doquery_username) or die(mysql_error());
So are things working or not? I got lost with what the situation is now with your last two posts ;-) (Sorry, I have been watching this thread closely)
Sorry, I'll reclarify
On first submit of form, no, it does not work and throws up the error "Query is empty"
If I refresh the page in Internet Explorer, and resubmit the data (via the IE prompt), the error is not thrown up, and everything is processed as it should.
Here is the whole PHP script before the MySQL query.
Excuse my comments. And the spelling. And the bad coding. And the lot, really
<?php
// Start session
session_start();
include("/home/site/public_html/resources/includes/functions.php");
// Assign variables from form
$username = $_POST['username'];
$email = $_POST['email'];
$emailconfirm = $_POST['emailconfirm'];
$password = $_POST['password'];
$passwordconfirm = $_POST['passwordconfirm'];
$dobday = $_POST['dobday'];
$dobmonth = $_POST['dobmonth'];
$dobyear = $_POST['dobyear'];
$nickname = $_POST['nickname'];
$regerror = ""; // Always blank the error var, because I'm silly and forget that.
// register them variables
session_register("username");
session_register("email");
session_register("emailconfirm");
session_register("password");
session_register("passwordconfirm");
session_register("dobday");
session_register("dobmonth");
session_register("dobyear");
session_register("nickname");
session_register("regerror");
// this is for us to call in the event we need to declare a 'fatal' error which must be reported back straight away
function fatalerror() {
header("Location: [edited because of silly forum autolink]");
exit;
}
// Check to see if the fields are empty
if($username == "") { $regerror .= " - The username is empty <br>"; }
if($email == "") { $regerror .= " - The email field is empty <br>"; }
if($emailconfirm == "") { $regerror .= " - The confirm e-mail is empty <br>"; }
if($password == "") { $regerror .= " - The password field is empty <br>"; }
if($passwordconfirm == "") { $regerror .= " - The confirm password is empty <br>"; }
if($dobday == "") { $regerror .= " - The date of birth day field is empty <br>"; }
if($dobmonth == "") { $regerror .= " - The date of birth month field is empty <br>"; }
if($dobyear == "") { $regerror .= " - The date of birth year field is empty <br>"; }
// force an error check - if a problem exists, go back to the form
if($regerror) { fatalerror(); exit; }
// check username and other fields for alpha numeracy thingy ma jiggy
if(eregi("[^a-z_0-9]",$username))
{
$regerror .= " - Your username contains invalid characters. Use only A-z and 0-9! <br>";
fatalerror();
exit;
}
if(eregi("[^a-z_0-9]",$password))
{
$regerror .= " - Your password contains invalid characters. Use only A-z and 0-9! <br>";
fatalerror();
exit;
}
if(eregi("[^a-z_0-9]",$nickname))
{
$regerror .= " - Your nickname contains invalid characters. Use only A-z and 0-9! <br>";
fatalerror();
exit;
}
$nickname = $username;
// Check to see if the username exists
mysql_select_db($mysqldatabase, $mysqlconnection);
$query_username = "SELECT id FROM users WHERE username='$username'";
echo $query_username."<br>";
$doquery_username = mysql_query($query_username) or die(mysql_error());
echo $doquery_username."<br>";
$numrows_username = mysql_num_rows($doquery_username) or die(mysql_error());
if($numrows_username > 0){
$regerror .= " - That username exists. Please choose another";
$username = "";
fatalerror();
exit;
}
[..]
I believe after you register your session variables, you still have to redefine the session back into variables...
session_register('username', 'email', 'emailconfirm', 'password', 'passwordconfirm', 'dobday', 'dobmonth', 'dobyear', 'nickname', 'regerror');
$_SESSION['username'] = $username;
$_SESSION['email'] = $email;
$_SESSION['emailconfirm'] = $emailconfirm;
// yadda, yadda, yadda...
Once you do this, you can use the variables in your query like you are trying to do.
"SELECT id FROM users WHERE username='$username'";
Otherwise, you would have to do something like:
"SELECT id FROM users WHERE username='$_SESSION['username']'";
Done that.
Now it still says:
SELECT id FROM users WHERE username='joely2'
Query was empty
Wheres that huge crying smiley 
I know this is going to sound silly, but..... Are you sure there is a user name in your users.username field that is joely2?
When your query comes back empty, it usually means just that. There was no result set...
Also, where are these values defined? (just out of curiosity.) I just wanted to make sure you were connecting to the right DB. (In case you had a users table in two different DBs)
$mysqldatabase, $mysqlconnection
I know this all sounds silly, but sometimes, you have to go back to basics to find problems you think are more complex than they really are...
Next, what happens if you put in the name "joely2" instead of the variable in your SQL?
Lastly, move all of your connection, and SQL to a different page (without all of the error checking) and see if it queries things fine there...
Originally posted by DeltaRho2K
I know this is going to sound silly, but..... Are you sure there is a user name in your users.username field that is joely2?
That is what it is checking - to see if it is present. If not, great. If it is, stop and report back.
This error is occuring with the bit of script in my signup that checks to see if someone has that username already
When your query comes back empty, it usually means just that. There was no result set...
Judging from the MySQL Help pages, it means there was no query passed in the mysql_query() bit, I think. But there must be, since I can echo it just before it actually does the query.
Also I can echo $username, $POST['username'] and $SESSION['username'] no problem at all during that stage.
Also, where are these values defined? (just out of curiosity.) I just wanted to make sure you were connecting to the right DB. (In case you had a users table in two different DBs)
$mysqldatabase, $mysqlconnection
Yup, connecting to right DB, as it works fine if I refresh the page (which is a very odd thing!). The MySQL connection info is defined in the include at the stop of the script (functions.php).
I know this all sounds silly, but sometimes, you have to go back to basics to find problems you think are more complex than they really are...
Yeah. I've also tried commenting out all of my stuff. Commenting out the MySQL queries, and it processes the registration fine.
I tried rewriting the MySQL query, using someone's suggestion from above:
mysql_select_db($mysqldatabase, $mysqlconnection);
$sql = "SELECT username FROM users WHERE username='$_POST['username']'"; //search for username
$result = mysql_query($sql) or die(mysql_error());
$num = mysql_num_rows($result);
// if($num > 0){
// $regerror .= " - That username exists. Please choose another";
// $username = "";
// fatalerror();
// exit;
// }
echo $num;
That does the same. "Query was empty".
However, upon a refresh, I get the HTML results, the data is added, and the number '0' at the top of the page (result of echo $num).
hat happens if you put in the name "joely2" instead of the variable in your SQL?
Well I tried that. And I also tried putting the Query into the mysql_query(); itself. Still the same error
lastly, move all of your connection, and SQL to a different page (without all of the error checking) and see if it queries things fine there...
I'll try that next!
Ok, it works fine on its own page.
But not with the rest of the script
Sooooooooooooooo. I need to check the rest of the script!
Ok, going a further step back.
The problem, which seems to miraculously fix itself when you refresh the page, I though may be linked to sessions somehow.
So I commented out all of my session stuff.
And low and behold, it works. First time.
So how the HECK were the sessions interferring with the MySQL query?
I could echo all the variables and there various forms remember - so what the heck is it? lol
<huge sigh>
I think I've sorted it.
As daft as it sounds, I put the 'session_register' bits in the wrong place.
After fiddling, this combo seems to work:
<?php
// Start session
session_start();
include("/home/site/public_html/resources/includes/functions.php");
// register them variables
session_register("username");
session_register("email");
session_register("emailconfirm");
session_register("password");
session_register("passwordconfirm");
session_register("dobday");
session_register("dobmonth");
session_register("dobyear");
session_register("nickname");
session_register("regerror");
// Assign variables from form
$username = $_POST['username'];
$email = $_POST['email'];
$emailconfirm = $_POST['emailconfirm'];
$password = $_POST['password'];
$passwordconfirm = $_POST['passwordconfirm'];
$dobday = $_POST['dobday'];
$dobmonth = $_POST['dobmonth'];
$dobyear = $_POST['dobyear'];
$nickname = $_POST['nickname'];
$regerror = ""; // Always blank the error var, because I'm silly and forget that.
[..]
?>
Tested it many times, and a few friends too.
Thanks to everyone, especially DeltaRho2K for your help mate 
I'll go and hide in the corner at the fact it was actually session's fault, and nothing to do with the mysql_num_rows. Still weird it wouldnt work though! :rolleyes:
You are welcome...
By the way, you're not 100% there...
The session actually works like this:
// Assign variables from form to variables
$username = $_POST['username'];
$email = $_POST['email'];
$emailconfirm = $_POST['emailconfirm'];
$password = $_POST['password'];
$passwordconfirm = $_POST['passwordconfirm'];
$dobday = $_POST['dobday'];
$dobmonth = $_POST['dobmonth'];
$dobyear = $_POST['dobyear'];
$nickname = $_POST['nickname'];
$regerror = "";
// register them variables in the session
session_register("username");
session_register("email");
session_register("emailconfirm");
session_register("password");
session_register("passwordconfirm");
session_register("dobday");
session_register("dobmonth");
session_register("dobyear");
session_register("nickname");
session_register("regerror");
// Assign the registered sessions back to variables for use later.
$_SESSION['username'] = $username;
$_SESSION['email'] = $email;
$_SESSION['emailconfirm'] = $emailconfirm;
$_SESSION['password'] = $password;
$_SESSION['passwordconfirm'] = $paswordconfirm;
$_SESSION['dobday'] = $dobday;
$_SESSION['dobmonth'] = $dobmonth;
$_SESSION['dobyear'] = $dobyear;
$_SESSION['nickname'] = $nickname;
$_SESSION['regerror'] = $regerror;
You may have trouble destroying the session variables the way you have it now... Also, I am not seeing how you could be assigning any values to your session_registers since you don't have the variables defined yet...
Try what I have here, and if that works, great (which it should )
If not, then keep going your way, but something just doesn't seem right about what you currently have...
by the way, you don't need to do session_register("variablename") and $_SESSION['variablename'], stick with one or the other
i have to say a couple of things, in my php book, and i tested this, it says :
1)
$mysql_numrows
not num_rows,
2)
you have to type sql query in this way,
$result = @($sql,$connection) or die("im too dumb to do the query thingamajigur!");
// with no space between sql and connect,
3) i have absolutely no idea why u guys use complications such as fatalerror() regerror, and junk like that, why dont u just type echo"sorry i couldn't do it"; and then include 'apagewithform.php';
Originally posted by Dax
i have to say a couple of things, in my php book, and i tested this, it says :
1)
$mysql_numrows
not num_rows,
2)
you have to type sql query in this way,
$result = @($sql,$connection) or die("im too dumb to do the query thingamajigur!");
// with no space between sql and connect,
3) i have absolutely no idea why u guys use complications such as fatalerror() regerror, and junk like that, why dont u just type echo"sorry i couldn't do it"; and then include 'apagewithform.php';
Not sure what you are referring to, but if your book is trying to use a PHP function called mysql_numrows, it is wrong, it is [man]mysql_num_rows[/man], it is a function of PHP, that is what we were talking about
you don't need the space in the mysql_query function, and you don't even need the $connection, mysql_query will take that last opened connection to mysql by default
Sometimes, it is nice to "trap" your errors, so you can do things like mail the admin or yourself telling you what time, date, page, etc... that the error occurred
i guess got lots to learn, even though mysql_numrows seems to work in my script, but you know, in my editor, when i type mysql_numrows it makes color black, and when i type mysql_num_rows it shows blue so ur prolly right...
thats kinda cool even though it'll take months for me to figure it out.. thx