There seems to be no easy solution to this problem.
You could keep a log of field names that were changed, you could keep a copy of the "old" records and find out by comparison which one was changed (tip: add a "valid-until" timestamp column to every row, or a "valid-from" column in addition).
You could keep a update-timestamp-field for every column, but this does not seem really feasible.
Depending on what you are planning to do, a log table might be the best solution. You could write an entry stating which user changed which column in which record (primary key) in which table ... and when.
Remember that you are trading auditing and security for speed with any of these solutions.
Cheers,
Steve
