Oracle 21c

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CREATE TABLE table_name (id) AS
SELECT COLUMN_VALUE
FROM   TABLE(SYS.ODCINUMBERLIST(12, 123, 123, 123, 123, 1234, 4444));
7 rows affected

SELECT  REGEXP_REPLACE(
          LISTAGG(A.ID, ',') WITHIN GROUP (ORDER BY A.ID),
          '([^,]+)(,\1)+',
          '\1'
        )
FROM    TABLE_NAME A


REGEXP_REPLACE(LISTAGG(A.ID,',')WITHINGROUP(ORDERBYA.ID),'([^,]+)(,\1)+','\1')


123,1234444


SELECT  TRIM(
          BOTH ',' FROM
          REPLACE(
            REGEXP_REPLACE(
              LISTAGG(',' || ID || ',') WITHIN GROUP (ORDER BY ID),
              '(,[^,]+,)\1+',
              '\1'
            ),
            ',,',
            ','
          )
        ) AS no_duplicates
FROM    TABLE_NAME


NO_DUPLICATES


12,123,1234,4444


SELECT  LISTAGG(DISTINCT ID, ',') WITHIN GROUP (ORDER BY ID) AS no_duplicates
FROM    TABLE_NAME


NO_DUPLICATES


12,123,1234,4444


SELECT  LISTAGG(ID, ',') WITHIN GROUP (ORDER BY ID) AS no_duplicates
FROM    (
  SELECT DISTINCT id FROM TABLE_NAME
)


NO_DUPLICATES


12,123,1234,4444