Understanding how Snowflake handles integrity constraints is vital, as it differs significantly from traditional transactional databases like PostgreSQL or SQL Server. In Snowflake, most constraints are not enforced by the system, with one major exception.

Enforcement vs. Documentation: Snowflake does not enforce PRIMARY KEY, FOREIGN KEY, or UNIQUE constraints during data loading or updates. If you define a primary key, Snowflake will still allow duplicate values to be inserted. The primary reason for including these is for documentation and metadata (Option C), allowing data analysts and BI tools to understand the intended relationships and schema design.

The NOT NULL Exception: The only integrity constraint that Snowflake actively enforces is NOT NULL (Option B). If a column is defined as NOT NULL, any attempt to insert or update a record with a null value in that column will result in an error.

Evaluating the Options:

Options A and D are incorrect because Snowflake does not actually enforce these constraints; it merely stores them as metadata.

Option E is incorrect because while keys can be used for clustering, defining them as constraints is not a prerequisite for specifying them as clustering keys.

Options B and C are the 100% correct reasons. They represent the practical application (enforcing data quality for nulls) and the architectural application (providing context for the data model).