Chapter 10 Exceptions

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Chapter 10 Exceptions Lab 10.1 Self-Review Answers A5: Questions Answers Comments 1) C If an exception is defined in the inner block, it can be raised in the inner block only. The outer block is not included in the scope of such an exception. 2) B Once an exception has been raised in the inner block and handled in the outer block, the control is passed to the enclosing environment. 3) B Once an exception occurs in the outer block, PL/SQL tries to find its handler in the outer block. PL/SQL will never search the inner block for the exception handler when the exception occurs in the outer block. 4) B In order to define an exception inside the body of the loop, you must define the PL/SQL block inside the body of the loop. Therefore, when an exception is raised, it will terminate the block, and the control will be transferred to the first executable statement after END. For example, FOR i IN 1..3 LOOP BEGIN SELECT first_name INTO v_first_name FROM student WHERE student_id = 123; EXCEPTION WHEN NO_DATA_FOUND THEN DBMS_OUTPUT.PUT_LINE ('Error'); END; END LOOP; In this case, if there is no student corresponding to student ID 123, the exception NO_DATA_FOUND is raised. This causes the PL/SQL block to terminate. However, as long as the value of the loop counter ranges between lower and upper limits, the PL/SQL block will be executed repeatedly. 5) B When you want to specify the same action for various exceptions, you can combine these exceptions in the single WHEN clause. The exceptions are included in the WHEN clause with the help of the OR operator.

Lab 10.2 Self-Review Answers

A5:	Questions Answers Comments 1) B A user-defined exception is declared and raised. The exception must be declared because it is defined by a programmer and is not provided by the system. The exception must be raised explicitly because it handles violation of application rules, not Oracle rules. For example, a negative value provided by a user for the student ID violates the application rule because an ID cannot be negative, yet it does not violate Oracle rules because a number can be negative. 2) B   3) B If a user-defined exception has been declared in the inner block, it can be raised in the inner block. However, it ceases to exist once the control is transferred to the outer block, and, as a result, it cannot be raised in the outer block. Any reference to such exception in the outer block will cause a syntax error. 4) B A user-defined exception behaves similarly to an Oracle built-in exception. 5) A The IF-THEN statement evaluates a condition that causes an application error. Once this condition yields TRUE, the RAISE statement raises a user-defined error associated with the application error. The IF-THEN statement by itself will not raise an exception. On the other hand, the RAISE statement by itself will always raise an exception.

Lab 10.3 Self-Review Answers

A5:	Questions Answers Comments 1) B Once an exception is raised in the declaration section of a block, the control is always transferred to the enclosing environment. In the case of an inner block, the control is transferred to the exception-handling section of the outer block. 2) B An exception encountered in the declaration section of any block causes the control to be transferred outside the block. When such a block is not enclosed by another PL/SQL block, the control is transferred to the host environment. This causes a syntax error. 3) A   4) B Re-raising an exception causes the control to transfer outside the block. In case of an inner block, the control is transferred to the exception-handling section of the outer block. 5) B

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