Hi,
ALTER VIEW statement allows you to change various properties of a** derived view.** This is why `ALTER VIEW base_view_name CACHE INVALIDATE`gives you an error since the view is a base view. To modify a base view, you would need to use ALTER TABLE statement instead.
For more information, please refer to the [Modifying a Base View](https://community.denodo.com/docs/html/browse/7.0/vdp/vql/creating_a_base_view/modifying_a_base_view/modifying_a_base_view) document.
There are two types of cache invalidation:
1. “Full” invalidation, which removes all the cached data for a view.
2. “Partial” invalidation that only removes the cached data that verifies a specified condition.
Please note that when a row is marked as invalid or reaches its time to live is not actually removed from the database. The row is in the cache, but when the view is queried, the Execution Engine does not retrieve it from the cache. Cache Maintenance Task” deletes the invalid or expired rows from the tables that hold the cached data of each view. For more information on this, please refer to the [Cache Maintenance Task](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/cache_module/cache_maintenance_task/cache_maintenance_task) document.
Hope this helps!
