In Snowflake, constraints such as PRIMARY KEY, UNIQUE, and FOREIGN KEY are not enforced by the system except for the NOT NULL constraint. Therefore, inserting duplicate values into a PRIMARY KEY column, inserting duplicate values into a column with a UNIQUE constraint, and inserting a value into a FOREIGN KEY column that does not match a value in the referenced column will not produce an error. However, trying to insert a NULL into a column that has a NOT NULL constraint will produce an error because Snowflake enforces the NOT NULL constraint.