DB2 10 for z/OS Database Administrator — Question 3

Which statement about NOT ENFORCED unique constraints is TRUE?

Answer options

• A. NOT ENFORCED unique constraints can not be defined on primary key columns
• B. The query optimizer will consider a NOT ENFORCED unique constraint when selecting an optimal data access plan
• C. When attempting to insert data that does not conform to a NOT ENFORCED unique constraint, a warning will be returned
• D. Storage requirements for a NOT ENFORCED unique constraint are no different than the storage requirements for a similar unique index

Correct answer: A

Explanation

Option A is correct because NOT ENFORCED unique constraints cannot be applied to primary key columns, which must always be enforced for data integrity. The other options are incorrect; the query optimizer does not consider NOT ENFORCED constraints, no warnings are issued for violations, and storage requirements differ from enforced unique indexes.