WITH temp0 AS
(SELECT LEVEL lv FROM dual CONNECT BY LEVEL <= 100)
SELECT MAX(REPLACE(sys_connect_by_path(str, ' '), ' ', '')) f1
FROM (SELECT str, row_number() over(ORDER BY ascii(str) ASC) rn
FROM (SELECT substr(t.vals, tv.lv, 1) str
FROM (SELECT '李富財a' AS vals, length('李富財a') AS cnt
FROM dual s
/* WHERE s.f = '李富財'*/) t
JOIN temp0 tv
ON tv.lv <= t.cnt))
START WITH rn = 1
CONNECT BY rn - 1 = PRIOR rn;