Manually Refresh:
Below is the syntax to manually refresh a materialized view where mv_name is the name of the materialized view.
REFRESH MATERIALIZED VIEW mv_name;
Enable Auto Refresh:
You can enable auto refresh of a materialized view using below syntax. Redshift refreshes materialized view as soon as possible after the underlying tables are updated.
ALTER MATERIALIZED VIEW mv_name AUTO REFRESH YES;
Schedule MV Refresh:
You can also schedule the sql statement to refresh materialized view using Redshift sql scheduler.