如何更新数据库中的数据[重复]

Question

This question already has an answer here:

• “Notice: Undefined variable”, “Notice: Undefined index”, and “Notice: Undefined offset” using PHP 28 answers
• How to display errors for my MySQLi query? [duplicate] 3 answers

I am new in PHP. I have to try to make a management system with PHP for learning purpose. there is a payment system which is two options one is "paid" and another is "paid later". Now I want to update from the site and use this code --

if(isset($_POST['pay_update'])){    
$payment  = $_POST['payment'];
$query   = "update doctorapp set payment='$payment' where id='$id'";
$result  = mysqli_query($connect, $query);
if($result){
echo "<script>alert('Update Success...')</script>";
echo "<script>window.open('patient-details.php', '_self')</script>";
}else{
echo "Update Failed...";
}

}

when I use 'id' it shows undefine index, and when I do not use 'id' it's working but change for all id. Now I want to know how I will update data for individual 'id'...?

enter code here

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Answer 1

You need to define the $id before your updated query,

EX :

$id = 1;

If not, you will get undefined error.

And as other people said in comments, your query is not safe at all, but as you are in learning phase, I would suggest you to learn with up to date tutorials, for example, for queries, use prepared statements and even better use it with PDO.