[Resolved] Query wont work inside function

Avochelm

I've had this problem before, but in other ways. I can't get things to work inside functions. I'm guess it's because of the way I am handling my variables, but can somebody please explain why the following does not work inside a function?

$db = mysql_connect($conf_db_host,$conf_db_username,
$conf_db_password);
mysql_select_db($conf_db_database,$db);

function usernametaken($username) {
  $sql="SELECT * FROM nnblog_users WHERE username='$username'";
  $result=mysql_query($sql);
  $num_rows=mysql_num_rows($result);

  if ($num_rows>0) {
    return true;
  }
  else {
    return false;
  }
}

The purpose of the function is to return true if a username has already been registered.

I get this error: Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in c:\program files\appserv\www\nnblog\register.php on line 9

laserlight

It probably means your query failed.
For debugging purposes, do some error checking, e.g.

$db = mysql_connect($conf_db_host,$conf_db_username, $conf_db_password)
	OR die('Could not connect to database');
mysql_select_db($conf_db_database,$db)
	OR die('Could not select database');

function usernametaken($username) {
	$sql = "SELECT * FROM nnblog_users WHERE username='$username'";
	$result = mysql_query($sql)
		OR die('Could not execute query');

if (mysql_num_rows($result) > 0) {
	return true;
}
else {
	return false;
}
}

Avochelm

I found the answer on: http://au.php.net/manual/en/functions.php

TO ALL BEGINNERS: (like me) You must define all global variables that you want to inside inside a function using global <var>; excluding superglobals. This is very unique to PHP.

Working Code:

function check_username($username) {
  global $db;

  $sql="SELECT * FROM nnblog_users WHERE username='$username'";
  $result=mysql_query($sql);
  $num_rows=mysql_num_rows($result);
  if ($num_rows>0) {
    return false;
  }
  else {
    return true; // returns true if username is available
  }
}

Avochelm

Just saw your post. 😃 Thanks, I'll remember that for future debugging.

laserlight

hmm... have you tried it?

Basically, "If no link identifier is specified, the last opened link is assumed", so having to declare the link variable global shouldnt be necessary, unless you're going to explicitly use it.

Avochelm

It seems to work when I apply it to an if statement.

I didn't only declare $db, I also declared $conf_db_prefix, which was a variable containing "nnblog_", but I left it out of my pastes for simplicty (when that was the problem lol). The full $sql variable looked like this:

$sql="SELECT * FROM ".$conf_db_prefix."users WHERE username='$username'";

To prove your point and my speculation, I removed the global $db; line and it worked fine.

casbboy

This is the ANSWER to my problem which none could figure out on other forums.

THANKS

Ryan