Oracle's puzzling behaviour with NLS_SORT and a simple regexp_like

Question

I ran into a weird behavior from Oracle this morning... And I can't understand why it acts this way from the docs. I'm sorry for the long post, but I want to make sure I'm understood. Oh, and make sure to read the note at the end before answering :)

The goal of the request is to return rows with 1 or more lowercase characters. For the sake of the example, my table will be:

CREATE TABLE "TEMP_TABLE" 
   ( "VAL" VARCHAR2(4000 BYTE) );
Insert into TEMP_TABLE (VAL) values ('00A00');
Insert into TEMP_TABLE (VAL) values ('00000');
Insert into TEMP_TABLE (VAL) values ('BC000');
Insert into TEMP_TABLE (VAL) values ('ABC00');
Insert into TEMP_TABLE (VAL) values ('AAAAA');
Insert into TEMP_TABLE (VAL) values ('abc00');

Using this SQL Request:

select val, 
case when regexp_like (val, '[a-b]') then 'MATCH' else 'NO' end from temp_table;

If the NLS_SORT value of the session is set to BINARY, oracle returns:

00A00   NO
00000   NO
BC000   NO
ABC00   NO
AAAAA   NO
abc00   MATCH

=>All good here: the only word containing a lowercase letter matches; the others don't.

but if NLS_SORT is set to FRENCH, the results are less understandable:

00A00   NO
00000   NO
BC000   MATCH
ABC00   MATCH
AAAAA   NO
abc00   MATCH

From what I can deduce, the regexp matches when there are characters other than A.

So my question is: Why would Oracle understand [a-z] as 'rows with letters that are not A' ?

Note 1: Specs: The database is under Oracle 10G(r2), and the Session's NLS Parameters are as follow:

NLS_CALENDAR    GREGORIAN
NLS_COMP        BINARY
NLS_CURRENCY    ¿
NLS_DATE_FORMAT DD/MM/RR HH24:MI
NLS_DATE_LANGUAGE   FRENCH
NLS_DUAL_CURRENCY   ¿
NLS_ISO_CURRENCY    FRANCE
NLS_LANGUAGE    FRENCH
NLS_LENGTH_SEMANTICS    BYTE
NLS_NCHAR_CONV_EXCP FALSE
NLS_NUMERIC_CHARACTERS  , 
NLS_SORT    FRENCH_M
NLS_TERRITORY   FRANCE
NLS_TIME_FORMAT HH24:MI:SSXFF
NLS_TIMESTAMP_FORMAT    DD/MM/RR HH24:MI:SSXFF
NLS_TIMESTAMP_TZ_FORMAT DD/MM/RR HH24:MI:SSXFF TZR
NLS_TIME_TZ_FORMAT  HH24:MI:SSXFF TZR

Note 2 : Yes, I could use regexp_like(val, '[[:lower:]]') . But I found out about this later on, and it doesn't explain the weird behaviour.

Answer 1

For better or worse, the sort ordering defined by nls_sort is being used to evaluate the [a-z] regexp. If you insert a,b,c,A,B, and C into temp_table and sort it under each setting you'll get the following:

SQL> alter session set nls_sort=BINARY;

Session altered.

SQL> select val,
  2  case when regexp_like (val, '[a-z]') then 'MATCH' else 'NO' end m
  3  from temp_table order by val;

VAL     M
------------------------- -------------------------
A       NO
B       NO
C       NO
a       MATCH
b       MATCH
c       MATCH

6 rows selected.

SQL> alter session set nls_sort=FRENCH;

Session altered.

SQL> select val,
  2  case when regexp_like (val, '[a-z]') then 'MATCH' else 'NO' end m
  3  from temp_table order by val;

VAL     M
------------------------- -------------------------
A       NO
a       MATCH
B       MATCH
b       MATCH
C       MATCH
c       MATCH

6 rows selected.

Since the upper case letters are "interleaved" with the lower case letters in the French setting it evaluates to true in Oracle's implementation.