Going along with the previous response, if you cannot come up with a unique constraint (single or multiple columns) then it really doesn't matter if duplicates are moved or not EDIT(in many cases, not all). If there is no way to tie back to the data uniquely, then it may be irrelevant. It sounds like you may have a natural unique key on your datetime column (assuming it is datetime and not date). Have you tried doing a distinct count on some of the columns?