PostgreSQL sequence based on another column

Question

Lets say I have a table as such:

Column   |     Type    |                        Notes
---------+------------ +----------------------------------------------         


        

Answer 1

PostgreSQL supports grouped unique columns, as such:

CREATE TABLE example (
    a integer,
    b integer,
    c integer,
    UNIQUE (a, c)
);

See PostgreSQL Documentation - Section 5.3.3

Easy :-)