select a.*,
       regexp_susbtr (comment, '.mmig+\w*|.mig+\w*') as selected
from   customer a
where  lower (comment) like %imm%g%'
or     lower (comment) like %im%g%;

regexp_susbtr (comment,'.mmig+\w*|.mig+\w*' <<=只拾取小写字母，什么是正确的编码，拾取任何小，大或混合字母
请参阅REGEXP_SUBSTR文档

...
match_param参数记录为：

• match_param是数据类型为VARCHAR2或CHAR的字符表达式，允许您更改函数的默认匹配行为。

match_param的值可以包含以下一个或多个字符：

• 'i'指定不区分大小写的匹配，即使条件的确定排序规则是区分大小写的。

因此，您需要：

SELECT a.*,
       REGEXP_SUBSTR(comment, '\w*mig\w*', 1, 1, 'i') AS selected
FROM   customer a
WHERE  REGEXP_LIKE(comment, 'im\w*?g', 'i');

其中：

• \w*mig\w*将匹配零个或多个（尽可能多的）单词字符，然后是子字符串mig，然后是零个或多个（尽可能多的）单词字符，'i'匹配参数使匹配不区分大小写。
• 'im\w*?g'匹配子串im，然后匹配零个或多个单词字符（尽可能少），然后匹配g子串，'i'匹配参数使匹配不区分大小写。

什么是%的替代方法，以查找regexp_substr和regexp_like之间的任何字母m和g
如果你想要单词字符a到z和0到9在任何情况下和_下划线，那么使用类似Perl的\w模式。
如果你只需要字母字符，那么使用POSIX字符类[[:alpha:]]或[a-zA-Z]或[a-z]，不区分大小写。
对于字母字符：

SELECT a.*,
       REGEXP_SUBSTR(comment, '[[:alpha:]]*mig[[:alpha:]]*', 1, 1, 'i') AS selected
FROM   customer a
WHERE  REGEXP_LIKE(comment, 'im[[:alpha:]]*?g', 'i');

或：

SELECT a.*,
       REGEXP_SUBSTR(comment, '[a-z]*mig[a-z]*', 1, 1, 'i') AS selected
FROM   customer a
WHERE  REGEXP_LIKE(comment, 'im[a-z]*?g', 'i');

这是一种选择;看看有没有用
一些样本数据：

SQL> with customer (col) as
  2    (select 'I am not an immigrant'                         from dual union all
  3     select 'I want immigration to be found'                from dual union all
  4     select 'Who is "imigrant"?'                            from dual union all
  5     select 'Yep, that is immigration we are talking about' from dual union all
  6     select 'What? IMMIGRATION on TV?'                      from dual union all
  7     select 'Imagine all the people'                        from dual union all
  8     select 'Awful migraine in my head'                     from dual union all
  9     select 'No such word here'                             from dual
 10    )

查询方式：

11  select col,
 12    regexp_substr(col, 'im.*g\w+', 1, 1, 'i') result
 13  from customer
 14  where lower(col) like '%im%g%';

COL                                           RESULT
--------------------------------------------- ---------------------------------------------
I am not an immigrant                         immigrant
I want immigration to be found                immigration
Who is "imigrant"?                            imigrant
Yep, that is immigration we are talking about immigration
What? IMMIGRATION on TV?                      IMMIGRATION
Imagine all the people                        Imagine

6 rows selected.

SQL>