我认为我有一个复杂的要求。

它是使用Oracle 10.2的组合排列，我能够使用笛卡尔联接来解决它，但是我认为它需要一些改进以使其更简单，更灵活。

主要行为。

输入字符串 ：“一二”

输出 ：’一’‘二’‘一二’‘二一’

对于我的解决方案，我将字符串数限制为5（请注意，输出是阶乘附近的数字）

SQL：

with My_Input_String as (select 1 as str_id, 'alpha beta omega gama' as str from dual )

--------logic-------

, String_Parse as (
                    SELECT REGEXP_SUBSTR(str, '[^ ]+', 1, ROWNUM) str
                    FROM My_Input_String
                    where rownum < 6 -- string limitation --
                    CONNECT BY level <= LENGTH(REGEXP_REPLACE(str, '([^ ])+|.', '\1') ) 
                  )

--------CRAP select need refactoring-------

select str from String_Parse
union
select  REGEXP_REPLACE(trim(s1.str||' '||s2.str||' '||s3.str||' '||s4.str||' '||s5.str), '( ){2,}', ' ') as str
from

(select str from String_Parse union select ' ' from dual) s1,
(select str from String_Parse union select '  ' from dual) s2,
(select str from String_Parse union select '   ' from dual) s3,
(select str from String_Parse union select '    ' from dual) s4,
(select str from String_Parse union select '     ' from dual) s5
where 
--
s1.str <> s2.str and s1.str <> s3.str and s1.str <> s4.str and s1.str <> s5.str
--
and s2.str <> s3.str and s2.str <> s4.str and s2.str <> s5.str
--
and s3.str <> s4.str and s3.str <> s5.str
--
and s4.str <> s5.str