Question: Which of the following statements regarding SQL constraints and their purposes is correct?

A) A CHECK constraint allows only numeric values to be entered into a column, ensuring that no other data types are permitted.
B) A FOREIGN KEY constraint establishes a relationship between two tables and ensures referential integrity by enforcing that values in one table correspond to values in another.
C) A UNIQUE constraint permits duplicate values in a column as long as they are not the primary key of the table.
D) A NOT NULL constraint can be applied to columns in a table to enforce that they must contain values; however, it does not apply to primary key columns.