How can I fix my codes?

Question

1.00/5 (1 vote)

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Always having

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, bool given in C:\xampp\htdocs\REVIEW\index.php on line 16

This is my code.

<?php
$servername = "localhost";
$username = "";
$password = "";
$remarks= "";
$con = mysqli_connect('localhost', 'root', '', 'firstdb');
if (!$con) {
  die("Connection failed: " . mysqli_connect_error());
}
if(!(empty($_POST["uname"]) && empty($_POST["pin"])))
{
    $UN=$_POST["uname"];
    $PW=$_POST["pin"];
    $sql = "SELECT * FROM users WHERE username=''".$UN." AND password=''".$PW. ";";
	$result = mysqli_query($con, $sql);
if (mysqli_num_rows($result) > 0) {
     header( "Location: Main.php" );
     }
   $remarks ="Sorry. Unrecognized username or password.Please try again";
 }
?>

<html>
  <body>
    <form action="index.php" method="post">
      <fieldset>
        <legend>Registration Details:</legend>
        <label for="uname">Username:</label><br>
        <input type="text" id="uname" name="uname" ><br>
        <label for="pin">PIN Code:</label><br>
        <input type="password" id="pin" name="pin" <br><br>
        <input type="submit" value="Register"> <br> 
       <label ><?php echo $remarks; ?></label><br></fieldset>
    </form> 
  </body>
</html>

What I have tried:

I tried to change some of it even check my semicolons and parenthesis, Im a beginner so it took me so long to fix.

Posted 9-Nov-20 6:00am

Kristine Viray

Updated 9-Nov-20 23:11pm

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Comments

Richard Deeming 10-Nov-20 5:07am

Your code is vulnerable to SQL Injection[^]. NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query.
PHP: SQL Injection - Manual[^]
PHP: Prepared statements and stored procedures - Manual[^]

Richard Deeming 10-Nov-20 5:08am

You are storing passwords in plain text. Don't do that.
Secure Password Authentication Explained Simply[^]
Salted Password Hashing - Doing it Right[^]

(And no, calling it a "pin" instead of a "password" doesn't change that.)

PHP even has built-in functions to help you do the right thing:
PHP: password_hash[^]
PHP: password_verify[^]

2 solutions

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Richard MacCutchan · Answer 1 · 2020-11-09T06:25:00

Solution 1

Mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in[^].

Posted 9-Nov-20 6:25am

Richard MacCutchan

Richard Deeming · Answer 2 · 2020-11-09T23:13:00

Quote:

PHP

$sql = "SELECT * FROM users WHERE username=''".$UN." AND password=''".$PW. ";";

You have not built your query correctly. You will get a MySQL syntax error when you try to execute this query.

Using a properly parameterized query will fix this, and fix your SQL Injection[^] vulnerability:
PHP: SQL Injection - Manual[^]
PHP: Prepared statements and stored procedures - Manual[^]

Now you just need to fix your insecure password storage.
PHP: password_hash[^]
PHP: password_verify[^]