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 '李富财a' AS vals, length('李富财a') AS cnt

FROM dual s

/* WHERE s.f = '李富财'*/) t

JOIN temp0 tv

ON tv.lv <= t.cnt))

START WITH rn = 1

CONNECT BY rn - 1 = PRIOR rn;