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<p><b><span style="font-size:22pt">Explaination 053: &nbsp;</span></b></p>

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	This statement returns the rows in the CUSTOMERS table that do not have a postal code. The correct syntax to check NULL values is usage of "IS NULL" clause. <br>
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	<p>
	  Incorrect Answers <br>
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	<p>
	  A: "CONTAINS NULL" is incorrect clause in Oracle. <br>
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	  B: This statement will just check if postal code equals to string '________'; <br>
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	  D: Usage of "IS NVL" is incorrect in Oracle. But there is a function NVL() you can use to process NULL values. <br>
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	  E: You can not use equal comparison to check whether value is NULL or not. Use construction "IS NULL" or "IS NOT NULL" to do that. <br>
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	<p>
	  OCP Introduction to Oracle 9i: SQL Exam Guide, Jason Couchman, p. 31-32 <br>
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	<p>
	  Chapter 1: Overview of Oracle Databases
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