Numbering all rows by an order

Question

I have a table with a two column PK. I'd like to add a new column, nid, which numbers each row (1,2,3...), based on a particular ORDER BY.

So:

x | y | z
3   7   2
1   4   1

When numbered by z ASC becomes:

x | y | z | nid
3   7   2 | 2
1   4   1 | 1

Can I do this in SQL (Postgres 9.4)?

Answer 1

If I understand correctly, you can just use row_number():

select x, y, z, row_number() over (order by z) as nid
from t;