SQL> CREATE TABLE t (x VARCHAR2(3));
  
Table created.
  
SQL> INSERT INTO t
  2  SELECT RPAD(ltr,3,ltr)
  3  FROM  (SELECT CHR(ROWNUM + 96) ltr 
  4         FROM   sys.all_users
  5         WHERE  ROWNUM <= 7)
  6  /
  
7 rows created.
  
SQL> SELECT x
  2  FROM   t
  3  /
  
X
---
aaa
bbb
ccc
ddd
eee
fff
ggg
  
7 rows selected.
  
SQL> SELECT  MAX(DECODE(ROWNUM,1,x))
  2  || ', ' || MAX(DECODE(ROWNUM,2,x))
  3  || ', ' || MAX(DECODE(ROWNUM,3,x))
  4  || ', ' || MAX(DECODE(ROWNUM,4,x))
  5  || ', ' || MAX(DECODE(ROWNUM,5,x))
  6  || ', ' || MAX(DECODE(ROWNUM,6,x))
  7  || ', ' || MAX(DECODE(ROWNUM,7,x)) combined
  8  FROM   t
  9  /
  
COMBINED
---------------------------------
aaa, bbb, ccc, ddd, eee, fff, ggg
  
SQL>