SQL  > CREATE TABLE DEBUG_TABLE
  2  (
  3    SLNO          NUMBER,
  4    MESSAGE       VARCHAR2(4000 BYTE),
  5    CREATED_DATE  DATE                            DEFAULT SYSDATE,
  6    CREATED_TIME  TIMESTAMP(6)                    DEFAULT SYSDATE
  7  );

Table created.

SQL  > CREATE UNIQUE INDEX index_debug1 ON debug_table (SLNO);

Index created.

SQL  > ALTER INDEX index_debug1 ADD COLUMN  MESSAGE; 
ALTER INDEX index_debug1 ADD COLUMN  MESSAGE
                         *
ERROR at line 1:
ORA-02243: invalid ALTER INDEX or ALTER MATERIALIZED VIEW option


SQL  >