Answer: INSERT OVERWRITE

`INSERT OVERWRITE` is the correct operation for overwriting existing data in a Delta table without altering its schema. It truncates the table or specified partitions before inserting new records. Other operations like `INSERT INTO` append data, `MERGE` allows for complex updates, inserts, and deletes, `COPY INTO` is for idempotent data ingestion, and `CREATE OR REPLACE TABLE` can replace the entire table, including its schema if necessary.

Author: LeetQuiz Editorial Team