Explanation:Exists is used to check whether an attribute value is null or not in conjunction with the where clause. 3. A lock that prevents the use of any tables in the database from one transaction while another transaction is being processed is called a
A. Database-level lock
B. Table-level lock
C. Page-level lock
D. Row-level lock
Answer:A
Explanation:Exists is used to check whether an attribute value is null or not in conjunction with the where clause. 3. A lock that prevents the use of any tables in the database from one transaction while another transaction is being processed is called a
A. Database-level lock B. Table-level lock C. Page-level lock D. Row-level lock
Explanation: Data base-level lock prevents the use of any tables in the data base from one transaction while other transaction is being processed.