如何使用 REGEXP_REPLACE 从每一端删除重复的逗号和修剪？

Question

我需要将几个字段连接在一起，这些字段可能为空，也可能不为空。我可能最终得到一个字符串，例如：',,c,,e,,' 我实际上想显示为 'c,e'。

我可以通过regexp_replace 和trim 的组合来获得这个：

with sd as (select 'a,b,c' str from dual union all
            select 'a' str from dual union all
            select null str from dual union all
            select 'a,,,d' from dual union all
            select 'a,,,,e,f,,'from dual union all
            select ',,,d,,f,g,,'from dual)
select str,
       regexp_replace(str, '(,)+', '\1') new_str,
       trim(both ',' from regexp_replace(str, '(,)+', '\1')) trimmed_new_str
from   sd;

STR         NEW_STR     TRIMMED_NEW_STR
----------- ----------- ---------------
a,b,c       a,b,c       a,b,c          
a           a           a              

a,,,d       a,d         a,d            
a,,,,e,f,,  a,e,f,      a,e,f          
,,,d,,f,g,, ,d,f,g,     d,f,g  

但我觉得它应该在单个 regexp_replace 中是可行的，只是我一生都无法弄清楚如何做到这一点！

有可能吗？如果有，怎么做？

Answer 1

查询：

with sd as (select 'a,b,c' str from dual union all
            select 'a' from dual  union all
            select null from dual union all
            select 'a,,,d,' from dual  union all
            select ',a,,,d' from dual  union all
            select ',a,,,d,' from dual  union all
            select ',,,a,,,d,,,' from dual  union all
            select ',a,,,,,e,f,,' from dual union all
            select ',,d,,f,g,,' from dual )
select str,
       regexp_replace(str, '^,+|,+$|,+(,\w)','\1') new_str
from   sd;

结果：

str             new_str
-----------------------
a,b,c           a,b,c
a               a
(null)          (null)  
a,,,d,          a,d
,a,,,d          a,d
,a,,,d,         a,d
,,,a,,,d,,,     a,d
,a,,,,,e,f,,    a,e,f
,,d,,f,g,,      d,f,g

模式：

  ^,+       matches commas at the beginning
  |         OR
  ,+$       matches commas at the end
  |         OR
  ,+(,\w)   matches several commas followed by a single comma and a word.

仅将上面的第一个子表达式替换为逗号和单词。

Answer 2

试一试：

with sd as (select 'a,b,c' str union all
            select 'a' union all
            select null union all
            select 'a,,,d' union all
            select 'a,,,,,e,f,,' union all
            select ',,,d,,f,g,,')
select str,
       regexp_replace(str, '(,){2,}', '\1', 1, 0) new_str,
       trim(both ',' from regexp_replace(str, '(,){2,}', '\1', 1, 0)) trimmed_new_str
from   sd;