What does the “refresh fields” button in the data source do?

The "refresh fields" button in a Data Studio data source is crucial for updating the data source's understanding of the underlying dataset. If you add new columns, delete existing columns, or change the data types of columns in your original data source (e.g., a Google Sheet or BigQuery table), Data Studio won't automatically recognize these changes. Clicking "refresh fields" forces Data Studio to re-examine the schema of the connected dataset and reflect those structural modifications within the data source. It does not update stale data in charts; that's handled by data refresh settings or manual refreshes of the report itself. It also doesn't save changes you make to the data source fields (like renaming them or changing their aggregation); those changes are saved automatically. Similarly, it doesn't specifically save updates to field names; it updates the structure of the fields based on the source.