Clarifcation - Delete files which are not in a mySQL TABLE - php

Question

Delete files which are not in a mySQL TABLE
The link above is to a Stack Overflow question with an answer that is (I believe) pretty close to what I'm looking for. I'm actually just seeking further clarification on the answer given.
The Question
I'm trying to delete files (picture files) in a folder only if they're
not present in a specific database table.
Just like a check of filenames and if they're present in the table
it's ok but if not delete them.
Any ideas how to do that?
The accepted answer
$result = mysql_query("SELECT filename FROM no_delete");
while($row = mysql_fetch_assoc($result)) {
$do_not_delete[] = $row['filename']; }
foreach(glob("*") as $filename) {
if (!in_array($filename, $do_not_delete)) {
//delete them
}
}
I'm not too savvy with PHP, but I don't believe they are specifying a folder path on the server here, are they? I'd like to be able to look inside a specific folder and check whether any images in that folder are within any database tables. If not, delete that image.

Answer 1

Before calling glob("*") just add a line chdir(""). Then you can search whichever directory you want to look at. I just went one level higher in the call below. You may specify whichever directory you want. Before doing a delete, just add an echo statement to $filename to verify if the correct files are being deleted.
chdir("../");
foreach(glob("*") as $filename) {
if (!in_array($filename, $do_not_delete)) {
//delete them
}

Answer 2

As described in this answer the first parameter, i.e. pattern, can contain the path to a directory relative to the current working directory of the script (which can be changed with chdir()) or an absolute path.
Consider this example from this tutorial page:
$dir = "/etc/php5/*";
// Open a known directory, and proceed to read its contents
foreach(glob($dir) as $file)
{
echo "filename: $file : filetype: " . filetype($file) . "<br />";
}