I wasn't thinking when designing the database and forgot to apply UNIQUE to a couple fields (field1, field2). Of course, after a couple thousand records it occurs to me and I want to fix it. However, trying to add UNIQUE at this point gives me the old #1062 duplicate entry error.

The problem is, that some of the records have no value in these fields, and some do, so this query isn't doing the trick.

Code MySQL:
SELECT field1, COUNT(*)
FROM table
GROUP BY field1

How do I find the records that have the duplicate(s)?