Chapter 6 Conditional Control: CASE Statements | Oracle PL/SQL Interactive Workbook (2nd Edition)


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	Oracle® PL/SQL® Interactive Workbook, Second Edition By Benjamin Rosenzweig, Elena Silvestrova
	Table of Contents

	Appendix A. Answers to Self-Review Questions

A1:

Questions	Answers	Comments
1)	C	The statements in a CASE construct are not executed sequentially. Rather, one group of statements or another will be selected to execute depending on how test conditions are evaluated.

A2:

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2)	B

A3:

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3)	B	The selector is evaluated only once, and the value of each expression is compared to the value of the selector sequentially.

A4:

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4)	A	The behavior of a searched CASE construct is similar to the behavior of an IF statement. In other words, if all conditions of the CASE construct evaluate to NULL and there is no ELSE clause present, the control will be passed to the first executable statement after END CASE.

A5:

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5)	A

A1:

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1)	A	A keyword here is expression. You will recall that an expression returns a single value.

A2:

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2)	C

A3:

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3)	B	Similar to CASE statements, there are CASE and searched CASE expressions.

A4:

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4)	A	The behavior of a CASE expression is similar to the behavior of a CASE statement. In other words, if all conditions of the CASE expression evaluate to NULL and there is no ELSE clause present, the expression returns NULL.

A5:

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5)	A	As mentioned earlier, the keyword here is expression. Because an expression returns a single value, it must return a single datatype.

A1:

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1)	A

A2:

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2)	B	The NULLIF function does the opposite of the NVL function. If the first expression is NULL, then NVL returns the second expression. If the first expression is not NULL, then NVL returns the first expression.

A3:

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3)	B	When the literal NULL is used in the first expression of the NULLIF function, it causes a syntax error.

A4:

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4)	A

A5:

Questions

Answers

Comments

As long as one of the expressions in the COALESCE function does not contain NULL, the COALESCE function executes successfully. For example,

 COALESCE(NULL, 5)

returns the value of 5. On the other hand,

 COALESCE(NULL, NULL)

causes a syntax error.


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