Explanation

In Delta Live Tables (DLT), the ON VIOLATION clause determines how constraint violations are handled. The specific syntax used in the question is:

CONSTRAINT valid_timestamp EXPECT (timestamp > '2020-01-01') ON VIOLATION FAIL UPDATE

CONSTRAINT valid_timestamp EXPECT (timestamp > '2020-01-01') ON VIOLATION FAIL UPDATE

The ON VIOLATION FAIL directive means that when any record violates the constraint, the entire job fails. This is a strict enforcement mechanism that ensures data quality by preventing any invalid data from being processed.

Key Points:

1. ON VIOLATION FAIL: This is the critical part - it causes the pipeline to fail when constraints are violated.

2. Comparison with other options:

   • Option A: Incorrect - Records are not just dropped and logged; the job fails.
   • Option B: Correct - The job fails when violations occur.
   • Option C: Incorrect - This would be more appropriate for ON VIOLATION DROP AND COUNT or similar quarantine mechanisms.
   • Option D: Incorrect - Records violating constraints are not added to the target dataset.

3. DLT Constraint Types:

   • ON VIOLATION FAIL: Job fails on violation
   • ON VIOLATION DROP ROW: Violating rows are dropped
   • ON VIOLATION DROP AND COUNT: Violating rows are dropped and counted

This behavior ensures data quality by enforcing strict validation before data enters the target dataset, which is crucial for production data pipelines.