When you run requests in Data Fetcher, the response data is transformed into Airtable fields and records. The response field mapping determines which fields from the API response are kept and how they are mapped to your output table. The response data transformation determines how nested arrays in the API response are handled.
The Airtable records can be written to the output table (and view) in two different ways:
Append - Add every record as a new record. This will not affect any existing records in the output table.
Update - Update existing records in the output table with the response records. If there are extra records remaining, create new records for these.