[SOLVED] DELETE and use !=....?

[Teck]

I'm having trouble deleting some data from a table of mine (about 3500 rows)...

 

Now I have another table "attachments" which has a list of all of the attachments I want to keep basically (about 2500 rows)...

 

What i need to do is delete any row from "forum_attachment" where "attachmentid" is not equal to any value in "attachid" Dunno if that makes any sense...

 

This is the code i have, it will give you a better idea as to what im trying to do

$query = "SELECT attachid FROM attachments ORDER BY id ASC";
$result = mysql_query($query) or die('Error:' . mysql_error());
while ($row = mysql_fetch_assoc($result)) {
$attachid = $row['attachid'];
$query = "DELETE FROM forum_attachment WHERE attachmentid != '$attachid'";
$result = mysql_query($query) or die('Error:' . mysql_error());
}

 

If someone can point me in the right direction i would be grateful...

[trq]

DELETE FROM forum_attachment WHERE attachmentid NOT IN(SELECT attachid FROM attachments);

[Teck]

Thanks!