Postgres 13

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
-- scale up: +1 col, +1 row
CREATE  TABLE tbl (column1 int, column2 text, column3 int, column4 text);
INSERT INTO tbl VALUES
  (1, 'value1', 3, 'foo')
, (2, 'value2', 4, 'bar')
, (3, 'value3', 5, 'baz');
3 rows affected

-- LATERAL VALUES
WITH cte AS (
   SELECT nu.*
   FROM   tbl t
   , LATERAL (
      VALUES
        (1, t.column1::text)
      , (2, t.column2)
      , (3, t.column3::text)
      , (4, t.column4)
      ) nu(rn, c)
   )
SELECT *
   FROM   (TABLE cte OFFSET  0 LIMIT 4) c1
   JOIN   (TABLE cte OFFSET  4 LIMIT 4) c2 USING (rn)
   JOIN   (TABLE cte OFFSET  8 LIMIT 4) c3 USING (rn)


rn
c
c
c


1
1
2
3

2
value1
value2
value3

3
3
4
5

4
foo
bar
baz


-- same with useful column names
WITH cte AS (
   SELECT nu.*
   FROM   tbl t
   , LATERAL (
      VALUES
        ('column1', t.column1::text)
      , ('column2', t.column2)
      , ('column3', t.column3::text)
      , ('column4', t.column4)
      ) nu(rn, c)
   )
SELECT * FROM (
   SELECT *
   FROM   (TABLE cte OFFSET  0 LIMIT 4) c1
   JOIN   (TABLE cte OFFSET  4 LIMIT 4) c2 USING (rn)
   JOIN   (TABLE cte OFFSET  8 LIMIT 4) c3 USING (rn)
   ) t (key, row1, row2, row3);


key
row1
row2
row3


column1
1
2
3

column2
value1
value2
value3

column3
3
4
5

column4
foo
bar
baz


-- hsotore
SELECT key
     , arr[1] AS row1
     , arr[2] AS row2
     , arr[3] AS row3
FROM  (
   SELECT x.key, array_agg(x.value) AS arr  -- ORDER BY t.ctid
   FROM   tbl t, each(hstore(t)) x
   GROUP  BY 1
   ) sub
ORDER  BY 1;


key
row1
row2
row3


column1
1
2
3

column2
value1
value2
value3

column3
3
4
5

column4
foo
bar
baz
key	row1	row2	row3
column1	1	2	3
column2	value1	value2	value3
column3	3	4	5
column4	foo	bar	baz