如果将日期格式更改为yyyy-MM-dd，代码将按预期工作。
检查下面的代码

WITH source AS (
  SELECT 
    a, 
    b,
    group_name,
    to_date(date,'MM/dd/yyyy') as date,
    order
  FROM VALUES 
  (1, 4, 'GFG1', '08/01/2000', 1),
  (1, 4, 'GFG1', '10/01/2000', 2),
  (1, 4, 'GFG1', '12/01/2000', 3),
  (2, 8, 'GFG2', '06/02/2000', 1),
  (4, 5, 'GFG3', '05/03/2000', 1),
  (4, 5, 'GFG3', '12/03/2000', 2)
  AS (a, b, group_name, date, order)
)
SELECT 
  a, 
  b, 
  group_name, 
  date, 
  order, 
  (DATE_DIFF(date, LAG(date, 1) OVER(PARTITION BY group_name ORDER BY date))) AS date_difference
FROM source