Databricks Data Engineer Associate Question 398
Single answerYou are working with a Delta table in Databricks and have enforced a unique constraint on a column. You are loading new data into this table using the MERGE statement. During the operation, some rows in the incoming data violate the unique constraint. If the MERGE statement specifies 'ON VIOLATION DROP ROW', what will be the behavior of the operation?
- A
The entire MERGE operation will fail, and no rows will be written to the table.
- B
Only the rows that violate the unique constraint will be dropped, and the rest of the valid rows will be written to the table.
- C
The rows that violate the unique constraint will overwrite the existing rows in the table.
- D
The rows that violate the unique constraint will be written to a separate error log for further analysis.
Show answer and explanation
Correct answer: B
Explanation
'ON VIOLATION DROP ROW' is used in Delta Lake operations to handle constraint violations by dropping only the rows that fail the constraint checks. This ensures that the rest of the valid rows are processed and written to the table without affecting the entire operation. It does not overwrite data or log the violating rows; instead, it silently drops them.
- A. Incorrect.
This is incorrect. 'ON VIOLATION DROP ROW' ensures that only the rows violating the constraint are dropped, not the entire operation.
- B. Correct.
This is correct. 'ON VIOLATION DROP ROW' drops only the rows violating the constraint and allows the valid rows to be written to the table.
- C. Incorrect.
This is incorrect. 'ON VIOLATION DROP ROW' does not overwrite any data; it simply drops the rows violating the constraint.
- D. Incorrect.
This is incorrect. 'ON VIOLATION DROP ROW' does not write the violating rows to an error log; it drops them entirely.