Oracle Certification Exam Question:
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Explain Which two statements are true regarding constraints? (Choose two.)
A. A foreign key cannot contain NULL values
B. A columns with the UNIQUE constraint can contain NULL values
C. A constraint is enforced only for the INSERT operation on a table
D. A constraint can be disabled even if the constraint column contains data
E. All constraints can be defined at the column level as well as the table level

Answer:

B. A columns with the UNIQUE constraint can contain NULL values
D. A constraint can be disabled even if the constraint column contains data

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Explain Which statements are correct regarding indexes? (Choose all that apply.)
A. When a table is dropped, the corresponding indexes are automatically dropped
B. A FOREIGN KEY constraint on a column in a table automatically creates a nonunique key
C. A nondeferrable PRIMARY KEY or UNIQUE KEY constraint in a table automatically creates a
unique index
D. For each data manipulation language operation performed, the corresponding indexes are
automatically updated

Explain Which two statements are true regarding views? (Choose two.)
A. A subquery that defines a view cannot include the GROUP BY clause
B. A view is created with the subquery having the DISTINCT keyword can be updated
C. A view that is created with the subquery having the pseudo column ROWNUM keyword cannot
be updated
D. A Data Manipulation Language (DML) operation can be performed on a view that is created
with the subquery having all the NOT NULL columns of a table