Oracle 11g Release 2

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE LIST 
    (FirstName varchar2(4), LastName varchar2(4))
;

INSERT ALL 
    INTO LIST  (FirstName, LastName)
         VALUES ('Ken', 'Chan')
    INTO LIST  (FirstName, LastName)
         VALUES ('John', 'Ng')
    INTO LIST  (FirstName,LastName)
         VALUES ('Joe', 'Lam')
             INTO LIST  (LastName)
         VALUES ('Lam')
             INTO LIST  (FirstName)
         VALUES ('Joe')
SELECT * FROM dual
;
5 rows affected

SELECT LastName || (CASE WHEN LastName IS NOT NULL AND FirstName IS NOT NULL THEN ',' END) || FirstName as FullName
FROM LIST;


FULLNAME


Chan,Ken

Ng,John

Lam,Joe

Lam

Joe