What happens if the 'persist_for' parameter is not set in a persistent derived table?

When the 'persist_for' parameter is not set in a persistent derived table, the behavior of the table is determined by Looker's built-in default settings for expiration. In such cases, the system implements a predefined expiration period for the table, meaning that it will automatically expire and be refreshed based on those rules. This ensures that the data remains relevant and is updated periodically without manual intervention from the user.

The default expiration helps maintain performance by ensuring that old data does not persist indefinitely, potentially leading to stale results. Users can rely on this behavior to have a semi-regular refresh of the data, thereby balancing the need for fresh data against the overhead of managing the persistence of the table.