Update Old id with new

[SASPhile]

New_id     Old_id
1
2              1
3

New_id      Old_id           Updated_Id
1                                            2
2                  1                        2
3                                            3

Need help in updating the new_id when there is an old id exists. In the above case New_Id "2"  has old_id "1". So the updated_id is "2" for the new_ids "1" and "2". 

[tomrvincent]

You should explain how 'updated_id' is derived, especially since there isn't any visible connection between a new_id of 1 and an updated_id of 2.

[Reeza]

Usually you'd have dates attached to those as well to help define the order.