How to enable AI(accent insensitiv) for one column without changing session

Question

Following is my test SQL:
create table accent_test(col varchar2(10 char);
insert into accent_test values('INDIA');
insert into accent_test values('india');
insert into accent_test values('InDiÄ ');
Following SQL can only enable CI(Case insensitive), but can’t enable AI(accent insensitive):
select *
from accent_test
where NLS_UPPER(col, 'NLS_SORT=GENERIC_BASELETTER') LIKE NLS_UPPER('INDIA', 'NLS_SORT=GENERIC_BASELETTER')
COL
INDIA
india
Upper SQL can’t return the third row ‘InDiÄ’ which includes accent character.
I know following SQL can enable AI by changing the session. However it will change the whole session and other columns in one table:
SQL> ALTER SESSION SET NLS_COMP=LINGUISTIC;
SQL> ALTER SESSION SET NLS_SORT=GENERIC_BASELETTER;
Is there any solution to enable AI for only one column without changing the session?

Answer 1

convert(<Any Chinese Character>, 'US7ASCII') will all return same character '?'.might be an matter of using the right characterset:
SQL> select 'ä' str, convert('ä', 'JA16SJIS') converted_str from dual union all
select 'á', convert('á', 'JA16SJIS') from dual union all
select 'â', convert('â', 'JA16SJIS') from dual union all
select 'à',  convert('à', 'JA16SJIS') from dual
STR CONVERTED_STR
ä   a           
á   a           
â   a           
à   a           
4 rows selected.