XF 2.0 Searching for blank customer user fields


Hi, my forum requires an active membership with a particular facebook group. Before we started a manual approval process based on facebook name and checking the group list there were a handful of members that I don't think had that field filled out (it is now a required field at registration). I would like to search for blank entries in the custom user field that I created. I did try it through phpMyAdmin but my SQL is rusty.

Also, I would like to run regular (weekly) "reports" that I can get into excel (csv, etc.) of the current website member list and the customer user field. With this I can pulug it into excel and setup some formulas to check for matches against another sheet that we copy from the facebook member roster (that's outside the scope of the question but detail added to hopefully aid in context)

Would this be something I would be able to do with a php file and password protect it in a director or will I have to manually go into phpMyAdmin and run the query and then export it.

So. long story short.
1) What is the best way to search for a null value in a blank custom user field
2) What is the best way to get a custom report of all users that shows data from the custom user field