Databricks Data Engineer Associate Question 348
Select 2A data engineer is using the COPY INTO statement to load data from a cloud storage location into a Delta table. Despite running the COPY INTO command multiple times, no duplicate data appears in the target Delta table. What could be the reason for this behavior?
- A
The Delta table enforces a unique constraint on the target column.
- B
COPY INTO uses file metadata to track files that have already been loaded.
- C
The target Delta table has a primary key defined, preventing duplicates.
- D
COPY INTO automatically ignores files that have already been processed based on their file paths.
- E
The COPY INTO statement includes an optional WHERE clause that filters duplicates.
Show answer and explanation
Correct answers: B, D
Explanation
The COPY INTO command prevents duplicates by tracking the file metadata (e.g., file paths and modification times) of files that have already been processed. If a file has been loaded previously, COPY INTO skips it in subsequent runs, ensuring that no duplicate data is added to the target Delta table. This behavior is independent of any unique constraints or primary keys, which Delta tables do not natively support.
- A. Incorrect.
Delta tables do not enforce unique constraints on columns by default. This is not the reason why duplicates are avoided.
- B. Correct.
COPY INTO tracks file metadata (such as file paths and modification times) to ensure that the same file is not loaded multiple times. This is one of the reasons why no duplicate data appears.
- C. Incorrect.
Delta tables do not natively support primary keys. Therefore, this is not the reason duplicates are avoided.
- D. Correct.
COPY INTO uses the file path to identify files that have already been processed. If the same file is referenced in subsequent COPY INTO commands, it is skipped to prevent duplication.
- E. Incorrect.
The WHERE clause in COPY INTO is used to filter the data being loaded, but it does not prevent duplicates unless explicitly designed to do so. This is not automatically the reason for avoiding duplicates.