Oracle 18c

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ALTER SESSION SET NLS_COMP=BINARY;
ALTER SESSION SET NLS_SORT=BINARY;
SELECT *
FROM   NLS_SESSION_PARAMETERS
WHERE  parameter IN ( 'NLS_COMP', 'NLS_SORT' );


PARAMETER
VALUE


NLS_SORT
BINARY

NLS_COMP
BINARY


SELECT regexp_count('OOO', '[a-z0-9]', 1, 'c' ) AS COUNT_AZ,
       regexp_count('OOO', '[[:lower:][:digit:]]', 1, 'c' ) AS count_lower
FROM   DUAL;


COUNT_AZ
COUNT_LOWER


0
0


ALTER SESSION SET NLS_COMP=ANSI;
ALTER SESSION SET NLS_SORT=GERMAN_AI;
SELECT *
FROM   NLS_SESSION_PARAMETERS
WHERE  parameter IN ( 'NLS_COMP', 'NLS_SORT' );


PARAMETER
VALUE


NLS_SORT
GERMAN_AI

NLS_COMP
ANSI


SELECT regexp_count('OOO', '[a-z0-9]', 1, 'c' ) AS COUNT_AZ,
       regexp_count('OOO', '[[:lower:][:digit:]]', 1, 'c' ) AS count_lower
FROM   DUAL;


COUNT_AZ
COUNT_LOWER


3
0


ALTER SESSION SET NLS_SORT=GERMAN_CI;
SELECT regexp_count('OOO', '[a-z0-9]', 1, 'c' ) AS COUNT_AZ,
       regexp_count('OOO', '[[:lower:][:digit:]]', 1, 'c' ) AS count_lower
FROM   DUAL;


COUNT_AZ
COUNT_LOWER


3
0


ALTER SESSION SET NLS_SORT=FRENCH_CI;
SELECT regexp_count('OOO', '[a-z0-9]', 1, 'c' ) AS COUNT_AZ,
       regexp_count('OOO', '[[:lower:][:digit:]]', 1, 'c' ) AS count_lower
FROM   DUAL;


COUNT_AZ
COUNT_LOWER


3
0