Which constraint can be defined only at the column level?
A.
UNIQUE
B.
NOT NULL
C.
CHECK
D.
PRIMARY KEY
E.
FOREIGN KEY
Explanation:
the NOT NULL constraint can be specified only at the column level, not at the table level.
Incorrect answer:
A:
UNIQUE can be define at table level
C:
CHECK can be define at table level
D:
PRIMARY KEY can be define at table level
E:
FOREIGN KEY can be define at table level
Refer: Introduction to Oracle9i: SQL, Oracle University Study Guide, 10-8