Updating neighboring records in no key table

Question

I have Table1 with 3 fileds: Field1, Field2, Field3. There is not key in the table.
I need to do the following:
If the Field2 equals 'A', the same field of the next record should be set to 'B'.
If the Field3 equals 'F', the same field of the previous record should be set to 'E'
For example:
Field1 Field2 Field3
=====  =====  =====
123     A    D
124     R    F
123     N    M
121     A    F
123     C    B          Should become
Field1 Field2 Field3
=====  =====  =====
125     A    E
126     B    F
123     N    E
121     A    F
124     B    B          Please advise on how to do this.
Thanks.

Answer 1

A natural order to rows in an Oracle heap table is a complete fallacy. If my table space has 100 blocks and my table starts at block 40 and goes to block 45, then someone drops or truncates a table at block 20, now my table takes an extent and is allocated blocks 20 through 25. Now when I select from the table and Oracle does a full table scan, I am likely to get rows from blocks 20 - 25 before the rows from blocks 40-45. Of course if rows are deleted and more rows inserted, then this too will affect the order in which rows are returned.
There is no guarantee that Oracle will return rows in the order in which they were inserted.
So, you need information in the row to tell you the sequence in which to return them.