Ok, what I am trying to do is create a page where someone can sign students up for classes. First, they select the student. Then, a table comes up with periods. Each "period" has a corresponding list of available classes. The person would select an available class and that would assign that particular class to that student for that period.

Well, right now, to do this, I am updating the null values in that student's period. This seems to be working fine.

But, let's say the student already has a class picked for that period. Can I have it so that the first option selected is that class and it says "(already scheduled)" right before that option in the select box. And then, it would go on to list the available classes for that time, but it wouldn't list the one already selected. How can I go about doing that?