Oracle 21c

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ALTER SESSION SET NLS_TERRITORY = 'Spain';
CREATE TABLE table_name (field_name NUMBER(9,2));
INSERT INTO table_name (field_name)
SELECT   0.22 FROM DUAL UNION ALL
SELECT 123    FROM DUAL UNION ALL
SELECT  15.55 FROM DUAL;
3 rows affected

SELECT field_name,
       TRIM(
         TRAILING '.' FROM
         TO_CHAR(
           field_name,
           'FM99999990D99',
           'NLS_NUMERIC_CHARACTERS= ''.,'''
         )
       ) AS formatted_value
FROM   table_name;


FIELD_NAME
FORMATTED_VALUE


,22
0.22

123
123

15,55
15.55