Updating a database with simple php and mysql - php

Question

I have a VERY simple form that is not working. What I am trying to accomplish is when the user clicks the update button, they are presented with a form filled in with the information. When they change the information and click update, they are sent back to the main form with all of their changes presented. Everything works but the update. When you change something and click update, nothing is changed. Here is the update form code:
<h4>Update Record</h4>
<?PHP
$con=mysqli_connect("localhost", "root", "", "customers");
//check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysql_connect_error();
}
?>
<form action="update_process.php" method="get">
Band: <input type="text" name="artist" value="<?php echo $_GET['artist'] ?>"/><br/>
Album: <input type="text" name="title" value="<?php echo $_GET['title'] ?>" /><br/>
Format: <select name="format">
<option value="Compact Disc" name="compact disc">compact disc</option>
<option value="Album" name="album">album</option>
<option value="Cassette" name="cassette">cassette</option>
<option value="MP3" name="mp3">mp3</option>
</select><br/>
Notes: <TEXTAREA NAME="notes" ROWS="3" COLS="30"><?php echo $_GET['notes'] ?>
</TEXTAREA><br/>
<input type="submit" value="Update" />
</form>
And here is the code for the update_process.php file:
<?php
$artist = $_GET['artist'];
$title = $_GET['title'];
$format = $_GET['format'];
$notes = $_GET['notes'];
//create connection to DB
$con=mysqli_connect("localhost", "root", "", "customers");
//check connection
if (mysqli_connect_errno()) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
$sql = "UPDATE music SET title='$title', artist='$artist', format='$format', notes='$notes'
WHERE id='$id'";
if ($con->query($sql) === TRUE) {
header('Location:index.php');
} else {
echo "Error: " . $sql . "<br>" . $con->error;
}
?>

Answer 1

In the WHERE clause you says where id = '$id', but where is the $id value set?
I think $id does not have a value.

Answer 2

I see some problems with your code:
1 - where id $id defined?
2 - I guess id is an integer field, so the 's around $id are not needed;

Answer 3

You've mixed object based and function based programming. You started with function based, so I'll show you that way. To query a database, you need to run:
mysqli_query($con,$sql);
Rather than:
$con->query($sql)
There are a few other problems security wise with your code, but skip the rest of my answer if you don't care.
You're not checking to see whether those GET parameters exist before you use them. Use:
if(isset($_GET['artist'],$_GET['track'],...)) {...}
You're also not escaping your query strings, making your site vulnerable to SQL injection. Use:
$artist = mysqli_real_escape_string($con,$_GET['artist']);
Good luck! Just go read the PHP docs, making sure you either take object or function approach for the entire script.