Unique Constraint Using My Own Definition of "Equals"

[B C]

I have a column that contains characters. I would like to put a unique constraint on this column, using my own definition of "equal."

Here's what I mean. In my data, two values are equal if they differ only by white space or capitalization. For example:

abcdefg == ABCdEfG == A B CDEFG == abCDefG ... (you get the idea)

My goal is that the database should reject any new rows where this column already contains an "equal" value.

Currently, I am working around this problem by using PHP to remove white space and case information before the data gets inserted. Then, a typical unique constraint does the job of rejecting duplicates. But of course enforcing integrity constraints at the application level is bad design, and I lose the original user-input representation of the data.

How can I get MySQL to enforce this constraint?

- Bill