Sql 使用`lag()`获取上一个时间戳

我试图让第一步时间戳到秒步长，以计算在两个步骤post:/login_request和post:/login之间花费了多少时间，使用lag()，但它需要时间戳每一步，并添加它的下一个记录.

*-----------------------------------------------------------------------------------------*
| device_serial  |  device_gen |   status_code |   method              |   event_time     |
*-----------------------------------------------------------------------------------------*
| ABC345         |  i13        |  200          |  post:/login_request  | 3/3/24 23:10:05  |
| ABC345         |  i13        |  200          |  post:/login          | 3/3/24 23:10:10  |
| EFG456         |  i13        |  200          |  post:/login_request  | 3/3/24 18:37:25  |
| EFG456         |  i13        |  200          |  post:/login          | 3/3/24 18:37:28  |
| EFG456         |  i13        |  200          |  post:/login_request  | 3/3/24 21:58:44  |
| EFG456         |  i13        |  200          |  post:/login          | 3/3/24 21:58:48  |                                                                       
*-----------------------------------------------------------------------------------------* 

我的问题和100:

select
    device_serial, 
    device_gen, 
    status_code, 
    method, 
    event_time,
    lag(event_time) over(partition by device_serial, status_code order by event_time) as first_step_ts
from test_tbl

我得到的是:

*-----------------------------------------------------------------------------------------------------------*
| device_serial  |  device_gen |   status_code |   method              |   event_time     | prev_ts         |
*-----------------------------------------------------------------------------------------------------------*
| ABC345         |  i13        |  200          |  post:/login_request  | 3/3/24 23:10:05  |                 |
| ABC345         |  i13        |  200          |  post:/login          | 3/3/24 23:10:10  | 3/3/24 23:10:05 |
| EFG456         |  i13        |  200          |  post:/login_request  | 3/3/24 18:37:25  |                 |
| EFG456         |  i13        |  200          |  post:/login          | 3/3/24 18:37:28  | 3/3/24 18:37:25 |
| EFG456         |  i13        |  200          |  post:/login_request  | 3/3/24 21:58:44  | 3/3/24 18:37:28 |
| EFG456         |  i13        |  200          |  post:/login          | 3/3/24 21:58:48  | 3/3/24 21:58:44 |
*-----------------------------------------------------------------------------------------------------------* 

我真正想要的是:

*-----------------------------------------------------------------------------------------------------------*
| device_serial  |  device_gen |   status_code |   method              |   event_time     | prev_ts         |
*-----------------------------------------------------------------------------------------------------------*
| ABC345         |  i13        |  200          |  post:/login_request  | 3/3/24 23:10:05  |                 |
| ABC345         |  i13        |  200          |  post:/login          | 3/3/24 23:10:10  | 3/3/24 23:10:05 |
| EFG456         |  i13        |  200          |  post:/login_request  | 3/3/24 18:37:25  |                 |
| EFG456         |  i13        |  200          |  post:/login          | 3/3/24 18:37:28  | 3/3/24 18:37:25 |
| EFG456         |  i13        |  200          |  post:/login_request  | 3/3/24 21:58:44  |                 |
| EFG456         |  i13        |  200          |  post:/login          | 3/3/24 21:58:48  | 3/3/24 21:58:44 |
*-----------------------------------------------------------------------------------------------------------* 

有没有人能给我一些指导，告诉我怎样才能达到以上的效果.