Which two statements are true about constraints? (Choose two.)
A.
The UNIQUE constraint does not permit a null value for the column.
B.
A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.
C.
The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.
D.
The NOT NULL constraint ensures that null values are not permitted for the column.
Explanation:
B: A unique constraint can contain null values because null values cannot be compared to anything.
D: The NOT NULL constraint ensure that null value are not permitted for the column
Incorrect answer:
A:
statement is not true
C:
statement is not true
Refer: Introduction to Oracle9i: SQL, Oracle University Study Guide, 10-9