In order to append new data to a Delta table while keeping existing rows, which mode should you use in the write command?

Using the append mode in the write command is the appropriate choice for adding new data to a Delta table while preserving the existing rows. When you apply this mode, the new data is simply added to the end of the table, without altering or removing any of the already existing records. This is particularly useful in scenarios such as incremental data loading, where you want to continuously add new transactions or entries over time while retaining all previous data for reporting and analysis.

The other modes do not achieve this functionality. For example, the overwrite mode completely replaces the existing table data with the new data, which is not desirable in cases where you want to maintain the older records. Error mode would throw an error if the write operation cannot proceed, while the ignore mode would skip the write operation if there are existing rows with the same primary keys or identifiers, which means no new data would be added at all. Thus, using append ensures continuity and growth of the dataset in the Delta table.