Alter time_bucket in a continuous aggregate

I have created a continuous aggregate over a materialized view with time_bucket('1 day'). Can I use Alter Materialized View command to change the time bucket to 12 hours without losing old data in the materialized view? Its okay for me to have old data granular at 1 day and new one at 12 hours. I just don’t want to loose the aggregated data because I have deleted the raw data using a retention policy.

No, I don’t think you’ll be allowed.

Just create a second view with 12 hours and drop the first.

If you have deleted the raw data, try to simulate the raw data from your continuous aggregates. It’s still not possible to backfill it.