Can someone please explain the difference between
By Day date granularity on a timestamp column in a reflection.
From my tests, I am struggling to see the difference, both in terms of output rows and in terms of what type of timestamp level aggregations are accelerated when using either.
Original - would group by <timestamp_col>
By day - would group by cast(<timestamp_col> as date) → i.e. rolling up from timestamp to date
You can basically test by creating such two identical reflections and you should see the size diff in the UI (by_day should be obviously way smaller).
If there is no diff then your timestamp_col might be truncated (i.e. “yyyy-mm-dd 00:00:00”)