有两行样本数据。。。给你想要的解决方案带来挑战。但这里有一个查询，它为您提供了id的最低日期行：

WITH tab (id, mydate) 
AS
(
  SELECT 1, TO_DATE('2020-02-02 19:45:00','YYYY-MM-DD HH24:MI:SS') FROM DUAL union
  SELECT 1, TO_DATE('2020-02-02 20:00:00','YYYY-MM-DD HH24:MI:SS') FROM DUAL  
),
ordered_dates AS
(
SELECT 
       id, 
       mydate, 
       ROW_NUMBER() OVER (PARTITION BY id ORDER BY mydate) AS rn FROM tab
)
SELECT id, TO_CHAR(mydate,'YYYY-MM-DD HH24:MI:SS') FROM ordered_dates WHERE rn = 1;

美国/纽约时区是utc-4，所以当你把美国/纽约转换成utc时，你得到原来的时间+4小时，即 2020-02-03 01:00:00 UTC :

WITH t (id, mydate) 
AS
(
  SELECT 1, TO_DATE('2020-02-02 19:45:00','YYYY-MM-DD HH24:MI:SS') FROM DUAL union
  SELECT 2, TO_DATE('2020-02-02 20:00:00','YYYY-MM-DD HH24:MI:SS') FROM DUAL  
)
select
  TO_CHAR(MYDATE,'YYYY-MM-DD HH24.MI.SS') original_time,
  FROM_TZ(
     TO_TIMESTAMP(
        TO_CHAR(MYDATE,'YYYY-MM-DD HH24.MI.SS')
       ,'YYYY-MM-DD HH24.MI.SS'
     ),
     'AMERICA/NEW_YORK'
   )
   AT TIME ZONE 'UTC'
    as UTC_TIME
from t;

ORIGINAL_TIME       UTC_TIME
------------------- --------------------------------------
2020-02-02 19.45.00 2020-02-03 00:45:00.000000000 UTC
2020-02-02 20.00.00 2020-02-03 01:00:00.000000000 UTC

2 rows selected.

你不需要 to_timestamp(to_char(... 在这种情况下，使用cast更容易：

FROM_TZ(cast(MYDATE as timestamp),'AMERICA/NEW_YORK') AT TIME ZONE 'UTC'