Stripe the order of a PostgreSQL result set

Question

Let's say I have the following table:

create temp table test (id serial, number integer);
insert into test (number) 
values (5), (4), (3), (2), (1), (0);

If I sort by number descending, I get:

select * from test order by number desc;
id | number
---+--------
 1 | 5
 2 | 4
 3 | 3
 4 | 2
 5 | 1
 6 | 0

If I sort by number ascending, I get:

select * from test order by number asc;

6 | 0
5 | 1
4 | 2
3 | 3
2 | 4
1 | 5

How do I stripe the order so that it alternates between ascending and descending per row? for example:

6 | 0   or   1 | 5
1 | 5        6 | 0
5 | 1        2 | 4
2 | 4        5 | 1
4 | 2        3 | 3
3 | 3        4 | 2

Answer 1

Update

WITH x AS (
    SELECT *
         , row_number() OVER (ORDER BY number) rn_up
         , row_number() OVER (ORDER BY number DESC) rn_down
    FROM   test
    )
SELECT id, number
FROM   x
ORDER  BY LEAST(rn_up, rn_down), number;

Or:

...
ORDER  BY LEAST(rn_up, rn_down), number  DESC;

to start with the bigger number.

I had two CTE at first, but one is enough - simpler and faster.

Answer 2

Or like this (similar to the already given answer but slightly shorter :)

WITH x AS (
    SELECT *, row_number() OVER (ORDER BY number) rn, count(*) over () as c
    FROM test
    )
SELECT id, number
FROM x 
ORDER BY ABS((c + 1.5) / 2 - rn) DESC;

If the reverse order is needed then it should be

ORDER BY ABS((c + 0.5) / 2 - rn) DESC;