get_view_history.md

A use case for the get_view_history function is tracking changes and debugging issues with a view's definition.

Imagine a complex view used in several dashboards and reports. Suddenly, the reports start showing unexpected results. Using get_view_history, you can quickly:

1. Identify when the view definition changed: Retrieve the historical definitions of the view to pinpoint the exact time a modification was made that might have introduced the error.
2. Compare different versions: Analyze the differences between previous versions and the current definition to understand exactly what changed in the SQL query. This helps in identifying the root cause of the issue.
3. Revert to a previous version: If a problematic change is identified, having access to the historical definitions makes it easy to revert the view to a known good state while a fix is being developed.
4. Audit view changes: Track who made changes and when, enhancing accountability and control over critical data assets. This is particularly important for regulatory compliance and data governance.
5. Understand the evolution of a view: By examining the history, you can gain insights into how the view's logic has evolved over time, aiding in documentation and knowledge transfer.

Example: Let's say your view my_project.my_dataset.important_sales_view is producing incorrect totals. You suspect a recent change to the view's SQL is responsible. You could use get_view_history (assuming your project is in the US multi-region):

SELECT * FROM bigfunctions.us.get_view_history('my_project.my_dataset.important_sales_view');

This would return a table showing the different versions of the view's definition along with timestamps, allowing you to compare the SQL before and after the problem started occurring. This helps isolate the problematic change and restore a correct version quickly.