通过PHP运行时MYSQL错误消息，但通过DQ查询运行正常

I'm trying to figure out why the PHP code below gives me this error:

There was an error running the query

[You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'query2' at line 1]

If I run that query straight from MYSQL it runs no problem....
Please help, I've been staring at this code for the past 40 minutes...

if($db->connect_errno > 0){
    die('Unable to connect to database [' . $db->connect_error . ']');
}

$query2 = ("UPDATE phpbb_users SET user_password='$hashPW' WHERE user_id='$id' AND username='$username';");

if(!$result = $db->query(query2)){
    die('There was an error running the query [' . $db->error . ']');
}    

$mysqli->close();

Change

if(!$result = $db->query(query2)){

to

if(!$result = $db->query($query2)){
                         ^

$ is missing in front of $query2 variable

On a side note: your code in its current state is prone to sql-injections. Please consider using prepared statements.

You are missing a $ on the one line...

if ($db->connect_errno > 0) {
  die('Unable to connect to database [' . $db->connect_error . ']');
}

$query2 = ("UPDATE phpbb_users SET user_password='$hashPW' WHERE user_id='$id' AND username='$username';");

if (!$result = $db->query($query2)) {
  die('There was an error running the query [' . $db->error . ']');
}   

$mysqli->close();