Databricks Certified Data Engineer - Associate

Explanation

The correct answer is C. MERGE.

Why MERGE is the correct choice:

1. MERGE (UPSERT) operation: The MERGE command in Delta Lake allows you to perform upsert operations (update existing records and insert new ones) while avoiding duplicates.
2. Duplicate prevention: MERGE uses a matching condition to determine whether to update existing records or insert new ones, ensuring no duplicate records are written.
3. Conditional logic: You can specify conditions like WHEN MATCHED THEN UPDATE and WHEN NOT MATCHED THEN INSERT to handle existing and new records appropriately.

Why other options are incorrect:

• A. DROP: This command deletes a table or view, not for writing data while avoiding duplicates.
• B. IGNORE: While there is an IGNORE option in some contexts, it's not a standard Delta Lake command for avoiding duplicates during data writes.
• D. APPEND: This simply adds data to a table without checking for duplicates, potentially creating duplicate records.
• E. INSERT: This inserts new records without checking for existing duplicates, which can lead to duplicate data.

Example usage:

MERGE INTO target_table AS target
USING source_table AS source
ON target.id = source.id
WHEN MATCHED THEN UPDATE SET *
WHEN NOT MATCHED THEN INSERT *;

MERGE INTO target_table AS target
USING source_table AS source
ON target.id = source.id
WHEN MATCHED THEN UPDATE SET *
WHEN NOT MATCHED THEN INSERT *;

This MERGE statement ensures that if a record with the same ID exists in the target table, it gets updated; otherwise, a new record is inserted, effectively preventing duplicates.