WITH t AS
(
SELECT CHR(LEVEL + 47) v
  FROM dual
 WHERE LEVEL <= 10    -- 0 ~ 9
    OR LEVEL >= 18    -- A ~ Z
 CONNECT BY LEVEL <= 43
)
SELECT REPLACE(SYS_CONNECT_BY_PATH(v, '-'), '-') x
  FROM t
 WHERE LEVEL = 4
 CONNECT BY LEVEL <= 4
;