Databricks-DE-Pro Developing Code (Python/SQL) Practice Question
A Data Engineer needs to perform an 'upsert' operation on a Delta table. Which command provides the most efficient way to merge new data with existing records in a single transactional step?
⚠ Common exam trap
Candidates often choose manual 'delete' and 'insert' operations, which are not atomic. They fail to recognize 'MERGE INTO' as the standard, efficient, and transactional way to perform upserts.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
MERGE INTO target USING source ON condition WHEN MATCHED ...
The MERGE INTO command is the standard SQL construct for performing upserts in Delta Lake. It handles both updates to existing records and the insertion of new records based on a join condition. This single, atomic statement simplifies complex logic that would otherwise require multiple steps, ensuring that the target table remains in a consistent state throughout the entire upsert operation in high-concurrency production environments.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
INSERT INTO ... ON DUPLICATE KEY UPDATE
Why it's wrong here
This syntax is common in MySQL but is not supported in Spark SQL or Delta Lake. Attempting to use this will result in a syntax error. Databricks requires the MERGE INTO command, which is more powerful and designed specifically for the needs of large-scale distributed data processing in the Delta Lake ecosystem.
- ✗
UPDATE target SET ...; INSERT INTO target ...
Why it's wrong here
Performing updates and inserts separately is not atomic. In a multi-user environment, another process could read the table in a partially updated state. Furthermore, this approach requires two full table scans, which is significantly less efficient than a single MERGE INTO operation that performs both tasks during one pass over the data.
- ✓
MERGE INTO target USING source ON condition WHEN MATCHED ...
Why this is correct
MERGE INTO is the native Delta Lake SQL command for upserts. It efficiently processes updates and inserts in a single transaction. It is highly optimized for performance and ensures data integrity by utilizing the transaction log to confirm that the entire operation either succeeds as a whole or rolls back upon failure.
- ✗
OVERWRITE TABLE target SELECT * FROM source
Why it's wrong here
Overwriting a table replaces the entire dataset. This is not an upsert; it destroys any existing data that is not present in the new batch. This would lead to permanent data loss of all historical records not included in the current ingestion source, which is unacceptable for standard business reporting and data retention.
About these practice questions
This Databricks-DE-Pro question is part of Courseiva's 267-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Databricks exam blueprint
This Databricks-DE-Pro practice question is part of Courseiva's free Databricks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the Databricks-DE-Pro exam.