Hi Jiahui,

Yes, if they arrive at the same millisecond, they are perserved in the arriving order.

Best,
Jark



On Mon, 11 May 2020 at 23:17, Jiahui Jiang <qzhzm173227@hotmail.com> wrote:
Hello! I'm writing a SQL query with a OVER window function ordered by processing time.

I'm wondering since timestamp is only millisecond granularity.

For a query using over window and sorted on processing time column, for example,
```
SELECT col1, 
     max(col2) OVER (PARTITION BY col1, ORDER BY _processing_time_column)
FROM table
```

If 2 records have the same processing timestamp (they arrived the operator at the exact same millisecond), is the order guaranteed to be preserved after the window function? If not, what would to the recommended workaround to keep the order?

Thank you!
Jiahui