Oracle 21c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
ALTER SESSION SET NLS_TIMESTAMP_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF';
CREATE TABLE APPOINTMENT (
  A_DATETIME TIMESTAMP(9),
  CLIENT_ID  NUMBER,
  PET_ID     NUMBER,
  VN_ID      NUMBER
);
INSERT INTO APPOINTMENT (A_DATETIME, CLIENT_ID, PET_ID, VN_ID)
  VALUES (TO_DATE('2023-01-20 09:30', 'YYYY-MM-DD hh24:mi'), 1001, 10001, 801);
1 rows affected

SELECT * FROM APPOINTMENT;


A_DATETIME
CLIENT_ID
PET_ID
VN_ID


2023-01-20 09:30:00.000000000
1001
10001
801


ALTER TABLE appointment MODIFY a_datetime DATE;
SELECT * FROM APPOINTMENT;


A_DATETIME
CLIENT_ID
PET_ID
VN_ID


2023-01-20 09:30:00
1001
10001
801