Brian Moon has had his share of issues with connecting PHP to MySQL, but sometimes, it's harder to track down the problem than others. So, he decided to put a simple trick in place to help him (and the mysqladmin proc command) locate the offending query.
We use a class that I wrote for all of our access to mysql. Its basically a wrapper for mysql_connect, mysql_select_db, mysql_query, mysql_num_rows(), etc. One method to handle all of that. Lots of you probably have one of these objects or libraries. Anyhow, what I did was add a comment into the sql just before I run the query.
Now, mysqladmin proc has the request URI for every query in it. The MySQL slow query log does as well. I know this is a simple little thing, but man, is it useful.
This trick is a quick and easy way to help see what page it is that's causing the issue (since multiple pages can use one SQL call), but it can also be used to help track down other values effecting the SQL as well. Very handy.