PHP - Help In Php Mysql Password Change Code:

/* validate the username and the password */
if((!isset($_POST['username'])) || (strlen(trim($_POST['username'])) <5) || (trim($_POST['username']) != preg_replace("/[^a-zA-Z0-9\_]/", "", trim($_POST['username'])))) {	
	/* if  is bad */
	$my_error = 1;
}else{
	$username = mysql_real_escape_string(trim($_POST['username']));
}
/* END validating username */

/* validate the password */
if((!isset($_POST['password'])) || (strlen(trim($_POST['password'])) <5) || (trim($_POST['password']) != preg_replace("/[^a-zA-Z0-9\_]/", "", trim($_POST['password'])))){
	/* if  is bad */
	$my_error = 1;
}else{
	$password = trim($_POST['password']);
}
/* END validating password */

/* if any of the post variables are invalid send back to the form page */
if($my_error != 0) {	
	$_SESSION['error_message'] =$error_message;	
	header("Location: index.php");
	exit();
}


/* FUNCTION TO CREATE SALT */
function createSalt(){
	$string = md5(uniqid(rand(), true));
	return substr($string, 0, 3);
}

/* check to see if username is in the table if not send back to login */
$query01 = "SELECT * FROM registered_users WHERE username = '$username'";
$result01 = mysql_query($query01)  or die(mysql_error());

if(mysql_num_rows($result01) != 1) {	
	header("Location: index.php");	
	exit();
 }


$row = mysql_fetch_array($result01);
$salt = $row['salt'];
$hash = hash('sha256', $salt, $password);
$query02 = "SELECT id FROM registered_users WHERE username = '$username' AND password = '$hash'";
$result02 = mysql_query($query02)  or die(mysql_error());
if(mysql_num_rows($result02) !=1){ 
	header("Location: index.php");	
	exit();
}
$_SESSION['id'] = $row['id'];
$_SESSION['valid_user'] = "yes";
header("Location: admin02.php");	
exit();
?>

Hi, I'm new here and I should say, I am a raw amateur at PHP and MySQL. All I can do is look at how others do similar things and try and adapt it.

I have a MySQL table: Neil_Details. It has 4 columns: id, number, name, password.

I can enter number and name from a csv file automatically, no problem. id is the Primary Key and will auto_increment.

The column 'number' is the student numbers, name is their Chinese names.

I want to take the column number and generate a password from each number in the column password.  That's all!

$password = password_hash($number, PASSWORD_DEFAULT);

People tell me, "Don't use their student numbers," but once I know how to do this in principle, I can splice part of the number and Chinese name together somehow and make a more secure password.

I just want to learn how to do this in principle. Then I can do it for each class.

So far I have this, which doesn't seem to work, although I get no errors in /var/log/apache2/error.log

Could you please help me along a bit with some tips, pointers, links?

My index.php first calls '/makePassword/form.html.php'

This is called makePassword.php.

Thanks for any tips!

<?php
        //start PHP session
        session_start();
     
        //check if login form is submitted
        if(isset($_POST['gettable'])){
            //assign variables to post values
            $tablename = $_POST['tablename'];
            
// login to the database dbname=allstudentsdb
        include $_SERVER['DOCUMENT_ROOT'] . '/includes/studentdb.inc.php';
        
        $stmt = $pdo->prepare('SELECT * FROM ' . $tablename . ' WHERE number = :number');
                $stmt->execute(['number' => $number]);
                $password = password_hash($number, PASSWORD_DEFAULT);
                echo 'password is ' . $password;
                $stmt = $pdo->prepare('INSERT INTO ' . $tablename . ' (password) VALUES (:password)');
                try{
                        $stmt->execute(['password' => $password]);
     
                        
                    }
                    catch(PDOException $e){
                        $_SESSION['error'] = $e->getMessage();
                    }
               }
               echo 'Passwords made!';

// the input form to get the mysql table name
               header('location: ' . '/makePassword/form.html.php');
               ?>