Oracle® PL/SQL® Interactive Workbook, Second Edition By Benjamin Rosenzweig, Elena Silvestrova
Table of Contents
Appendix A. Answers to Self-Review Questions
Lab 17.1 Self-Review Answers
A1:
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1)
C
A2:
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2)
B
Once a trigger has been defined on a particular table, it fires implicitly when a triggering event occurs. By default, when a trigger is created it is also enabled. Once you disable a trigger, it will not fire when a triggering event occurs.
A3:
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3)
A
The WHEN condition controls when a trigger should fire. If such a condition does not evaluate to TRUE, the trigger will not fire.
A4:
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4)
C
A5:
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D
A trigger fires before or after a triggering event: INSERT, UPDATE, or DELETE. A SELECT operation is not a triggering event. It reads information from a triggering table without modifying it.
Lab 17.2 Self-Review Answers
A1:
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A
A2:
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B
A statement trigger fires once per DML statement issued. In other word, if there is a statement trigger that fires before an UPDATE statement is issued against a triggering table, it will fire once regardless of number of rows affected by the UPDATE statement.
A3:
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B
A4:
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B
It is important to remember that even though an INSTEAD OF trigger is defined on a view, it manipulates underlying database tables.
A5:
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B
An INSTEAD OF trigger can never be a statement trigger.
Lab 17.3 Self-Review Answers
A1:
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B
You cannot issue an SQL statement against the triggering table in the body of the trigger.
A2:
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B
Any SQL statement (INSERT, UPDATE, DELETE, and SELECT) against the triggering table inside the body of the trigger will cause a mutating table error.
A3:
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B
You are able to issue SQL statements against any table but the triggering table in the body of a trigger. In other words, it there is a trigger defined on the STUDENT table, you can issue a SELECT statement against the ZIPCODE table in the body of the trigger. This will not cause any error. However, if you issue a SELECT statement against the STUDENT table, you will get a mutating table error when the trigger fires. You will recall that a mutating table error is a runtime error and is not be detected by the PL/SQL compiler.
A4:
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C
A5:
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C
You will recall that a constraining table restriction is applicable to Oracle versions prior to 8i.
