The correct answer is A. NOT NULL .

For standard Snowflake tables, Snowflake enforces the NOT NULL constraint. Other constraints such as PRIMARY KEY, FOREIGN KEY, and UNIQUE can be defined, but they are generally informational and are not enforced for standard tables.

Why A is correct:

A NOT NULL constraint prevents NULL values from being inserted into the constrained column.

Example:

CREATE TABLE customers (

customer_id NUMBER NOT NULL,

customer_name STRING

);

Why the other options are incorrect:

B. PRIMARY KEY constraints are not enforced for standard Snowflake tables.

C. FOREIGN KEY constraints are not enforced for standard Snowflake tables.

D. UNIQUE constraints are not enforced for standard Snowflake tables.

Official Snowflake documentation reference:

Snowflake documentation explains that for standard tables, NOT NULL constraints are enforced, while unique, primary key, and foreign key constraints are not enforced.