postgresql - How to select from SQL table so even and odd rows would be in separate columns?

Question

There is a table ID in my PostgreSQL database.

select * from ID;

ID
1
2
3
4
5
6
7
8

I need to write a query that will give me this output:

id id 
1   2
3   4
5   6
7   8

Answer 1

There are no such things as even and odd rows. SQL tables represent unordered sets (well technically multi-sets).

Assuming id is the ordering, you can split them using aggregation like this:

select min(id), max(id)
from (select t.*, row_number() over (order by id) - 1 as seqnum
      from t
     ) t
group by floor(seqnum / 2)