Answer: NOT NULL

Based on the community discussion and Snowflake documentation, NOT NULL is the constraint that Snowflake enforces. The community discussion shows 100% consensus on answer B (NOT NULL) with upvoted confirmation that this is correct. Snowflake enforces NOT NULL constraints to ensure columns cannot contain null values. However, Snowflake does not enforce FOREIGN KEY, PRIMARY KEY, or UNIQUE KEY constraints - while these can be declared in table definitions for documentation purposes, Snowflake does not validate or enforce referential integrity or uniqueness for these constraint types. This aligns with Snowflake's design philosophy of prioritizing performance over complex constraint enforcement.

Author: LeetQuiz Editorial Team