Course: Principles of Database please solve it within 30 minutes. please please, please Thank you Single Choice Questions 11. Given a relation R and a condition f for selecting from relation R, the correct relational algebraic expression is ( ). A、R X R B、 R ⋈ R C、sf(R) D、 ∏f(R) 12. If relations R and S have a common attribute set Y, when executing , tuples that do not have matching values on attribute Y will be discarded. To avoid discarding those tuples, which operation should be used? ( ) A. Aggregation. B. Grouping. C. Outer union. D. Outer join. 13. To address the "lost update" problem, a transaction must obtain ( ) before updating a data set. A. Shared lock (S-lock). B. Exclusive lock (X-lock). C. Shared lock (S-lock) and exclusive lock (X-lock). D. Shared lock (S-lock) or exclusive lock (X-lock).
Course: Principles of
please solve it within 30 minutes. please please, please
Thank you
Single Choice Questions
11. Given a relation R and a condition f for selecting from relation R, the correct relational algebraic expression is ( ).
A、R X R B、 R ⋈ R C、sf(R) D、 ∏f(R)
12. If relations R and S have a common attribute set Y, when executing , tuples that do not have matching values on attribute Y will be discarded. To avoid discarding those tuples, which operation should be used? ( )
A. Aggregation. B. Grouping.
C. Outer union. D. Outer join.
13. To address the "lost update" problem, a transaction must obtain ( ) before updating a data set.
A. Shared lock (S-lock).
B. Exclusive lock (X-lock).
C. Shared lock (S-lock) and exclusive lock (X-lock).
D. Shared lock (S-lock) or exclusive lock (X-lock).
14. If, during the system operation, data stored on external storage is partially or completely lost due to hardware failure, it is referred to as ( ).
A. Media failure. B. Operational failure.
C. System failure. D. Transaction failure.
15. To ensure security, a purchasing officer can only query the product's product number, name, supplier, and price. To achieve this, the DBA can create a corresponding ( ) for the purchasing officer to query.
A. Table. B. Index. C. View. D. Cursor.
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