update mysql field

Hi all!
The thing i'm triing to achieve:
users can post forms on my site, but for security reasons they can't upload to the site, just post some remote url which then saved to a field in my mysql database (directly linked to images).
I would like to cache those images to my server. I already have a working function, and i can cache the images to the given folder on my server, and i can get the path to the image, but how do i update the mysql field (delete the old url in mysql and replace with the new path, to the cached image)?

This is the code for caching:

<?php
$db = mysql_connect("host", "name", "password");
mysql_select_db("mydatabase", $db);
$query  = "SELECT * FROM table WHERE something='somethingtwo'";
$result = mysql_query($query);
function cache_image($image_url){
	//replace with your cache directory
	$image_path = './cache/';
	//get the name of the file
	$exploded_image_url = explode("/",$image_url);
	$image_filename = end($exploded_image_url);
	$exploded_image_filename = explode(".",$image_filename);
	$extension = end($exploded_image_filename);
	//make sure its an image
	if($extension=="gif"||$extension=="jpg"||$extension=="png"){
		//get the remote image
		$image_to_fetch = file_get_contents($image_url);
		//save it
		$local_image_file  = fopen($image_path.$image_filename, 'w+');
		chmod($image_path.$image_filename,0755);
		fwrite($local_image_file, $image_to_fetch);
		fclose($local_image_file);	
	}
}

while($row = mysql_fetch_array($result, MYSQL_ASSOC))
{
cache_image($row['something_value']);
} 
mysql_close($db);
?>

PHP:

 

UPDATE table SET url='$newurl' WHERE something='somethingtwo' LIMIT 1;

Code (markup):

Should work perfectly, unless I've made a typo.

 

Thanks for the help! I will try it!