Which statement regarding NOT ENFORCED unique constraints is true?
A.
NOT ENFORCED unique constraints enforce uniqueness only for primary key columns.
B.
The query optimizer will consider a NOT ENFORCED unique constraint when selecting the
optimal data access plan.
C.
Storage requirements for NOT ENFORCED unique constraints are identical to storage
requirements for a unique index.
D.
When attempting to insert data that does not conform to the NOT ENFORCED unique
constraint, an error will be returned and the record will not be inserted.
In DB2® Version 10.5, support is added for NOT ENFORCED primary key and unique constraints. These informational constraints help the query optimizer to select optimal data access plans when index access to the data provides no additional benefit.
If you know that the data conforms to these constraints, you can use the NOT ENFORCED capability to help achieve two goals:
Improve performance, primarily in insert, update, and delete operations on the table
Reduce space requirements that are associated with enforcing a primary key or unique constraint
https://www.ibm.com/support/knowledgecenter/en/SSEPGG_10.5.0/com.ibm.db2.luw.wn.doc/doc/c0061153.html
I think answer is B.
0
0