You cannot change the ON COMMIT properties of a global temporary table if a materialized instance of the table exists.
- DELETE ROWS
- Delete the contents of an instance of a global temporary table when a transaction completes. DELETE ROWS clears an instance of a global temporary or volatile table of all rows. DELETE is the default.
- PRESERVE ROWS
- Preserve the contents of an instance of a global temporary table when a transaction completes. PRESERVE ROWS retains the rows in the table after the transaction commits.