Update image path - php

Question

I'm fairly new to PHP programming and I've looked around but I'm still confused. I'm trying to update the image path in my users table and I'm not quite sure how to do it. This is the code I have for putting the image into the database and it works to insert it in, but I'm not sure how to UPDATE the image picture path in my database to use the newly inserted image as opposed to the one the user selected when they created an account.
// Make sure we didn't have an error uploading the image
($_FILES[$image_fieldname]['error'] == 0)
or handle_error("the server couldn't upload the image you selected.",
$php_errors[$_FILES[$image_fieldname]['error']]);
// Is this file the result of a valid upload?
#is_uploaded_file($_FILES[$image_fieldname]['tmp_name'])
or handle_error("you were trying to do something naughty. Shame on you!",
"upload request: file named " .
"'{$_FILES[$image_fieldname]['tmp_name']}'");
// Is this actually an image?
#getimagesize($_FILES[$image_fieldname]['tmp_name'])
or handle_error("you selected a file for your picture " .
"that isn't an image.",
"{$_FILES[$image_fieldname]['tmp_name']} " .
"isn't a valid image file.");
// Name the file uniquely
$now = time();
while (file_exists($upload_filename = $upload_dir . $now .
'-' .
$_FILES[$image_fieldname]['name'])) {
$now++;
}
// Finally, move the file to its permanent location
#move_uploaded_file($_FILES[$image_fieldname]['tmp_name'], $upload_filename)
or handle_error("we had a problem saving your image to " .
"its permanent location.",
"permissions or related error moving " .
"file to {$upload_filename}");
$insert_sql = "UPDATE users set user_pic_path WHERE user_id = $user_id =
replace(user_pic_path, '$upload_filename', '$upload_filename' );
//insert the user into the database
mysql_query($insert_sql);
</code>
EDIT:
I was missing a " which I fixed and now there is no SQL error, it puts the picture into the database but does not replace the image path in the database. I've been messing with the $insert_sql but it still doesn't update the database with the new image path, what can I do? Here's my new update code:
<code>
$insert_sql = "UPDATE users WHERE user_id = $user_id set user_pic_path =
replace(user_pic_path, '$upload_filename', '$upload_filename')";
</code>

Answer 1

In the final lines, insert a test of your SQL:
$insert_sql = "UPDATE users WHERE user_id = $user_id set user_pic_path = replace(user_pic_path, '$upload_filename', '$upload_filename')";
// check the query
echo $insert_sql."<br />";
//insert the user into the database
mysql_query($insert_sql);
Then you can watch the query your about to run, test it in PHPMyAdmin, work out what it should be. It's worth doing for other key variables as well. Even better, you should write a "debug" function, that logs what's going on in a file on the server so that when an error occurs, you can track details of it, including values of key variables in every file.