Linguistic index with LIKE + LOWER

Question

Hi,
It seems that Oracle 11.2.0.1.0 is not able to use linguistic index when using the LIKE operator + LOWER function...
ALTER SESSION SET NLS_COMP='LINGUISTIC';
ALTER SESSION SET NLS_SORT='FRENCH_AI';
CREATE INDEX test_fai_idx
ON mytable(NLSSORT(LOWER(somefield), 'NLS_SORT=FRENCH_AI'));
SELECT *
FROM mytable
WHERE LOWER(somefield) LIKE 'gue%';
-- Table access FULL
DROP INDEX test_fai_idx;
ALTER SESSION SET NLS_COMP='BINARY';
CREATE INDEX test_bin_idx
ON mytable(LOWER(somefield));
SELECT *
FROM mytable
WHERE LOWER(somefield) LIKE 'gue%';
-- Index Range Scan
Questions:
-Will an upgrade to 11.2.0.2, 11.2.0.3 or 11.2.0.4 could solve that problem? (if anyone of you who have access to such a db and could make the test and report the result here, that will be much appreciated)
-Other ideas to help me?
I understand that using LOWER + AI seem strange since AI means accent-insensitive AND case-insensitive but, the software which run on the db use LOWER in all his SQL...
Thanks.
Paulo

Answer 1

create table test (nid number, name varchar2(30))
insert into test values(1, 'hügo')
ALTER SESSION SET NLS_COMP='LINGUISTIC';
ALTER SESSION SET NLS_SORT='FRENCH_AI';
select
from test
where
lower(name) like 'hug%'
no data found, full scan
create index idx_t on test(lower(name))
select
from test
where
lower(name) like 'hug%'
no data found, index range scan
drop index idx_t
create index idx_t on test(nlssort(lower(name), 'NLS_SORT=FRENCH_AI'))
select
from test
where
lower(name) like 'hug%'
no data found, full scan
Why should the index be used? You are looking for lower(name) but nlssort(lower(name), 'NLS_SORT=FRENCH_AI') indeed is something totally different:
select
nlssort(lower(name), 'NLS_SORT=FRENCH_AI') s
from test
S
3773325A000202020200
since
select
nlssort('hug', 'NLS_SORT=FRENCH_AI') s
from test
is
S
3773320002020200
you might recongize that it is not possible to do a like with nlssort.