Using Null - Revision history

79.191.79.150 at 06:52, 8 September 2012

2012-09-08T06:52:21Z

2012-08-15T11:58:50Z

2012-07-27T01:34:44Z

2012-07-24T14:39:44Z

2012-07-24T13:27:19Z

2012-07-20T00:25:36Z

2012-07-19T23:55:46Z

2012-07-19T03:20:31Z

2012-07-19T01:38:05Z

2012-07-19T01:17:50Z

@@ Line 99: / Line 99: @@
 List the teachers who have NULL for their department.
 <div class='hint' title='Why we cannot use ='>
-You might think that the phrase dept=NULL would work here. It doesn't. This is because NULL "propogates". Any normal expression that includes NULL is itself NULL, thus the value of the expressions 2+NULL and party || NULL and NULL=NULL for example are all NULL.
+You might think that the phrase dept=NULL would work here. It doesn't. This is because NULL propagates. Any normal expression that includes NULL is itself NULL, thus the value of the expressions 2+NULL and party || NULL and NULL=NULL for example are all NULL.
 <div title="That's not a proper explanation." class='hint'>

← Older revision		Revision as of 11:58, 15 August 2012
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	<div class="lsclear">Clear your results</div>		<div class="lsclear">Clear your results</div>

−	[[Using Null Quiz]]	+	<p><div class="quizlink">[[Using Null Quiz]]</div></p>

@@ Line 84: / Line 84: @@
 [[Selecting NULL values.]]
-<div class="summary">Summary</div>
+<div class="progress_panel"><div>
+   <div class="summary">Summary</div>
-<div class="progressbarbg">
+   <div class="progressbarbg">
-  <div class="progressbar"></div>
+     <div class="progressbar"></div>
-</div>
+   </div>
 <div class='extra_space' style='width:1em; height:2.5em;'></div>

@@ Line 234: / Line 234: @@
 </source>
 </div>
 [[Using Null Quiz]]

← Older revision		Revision as of 13:27, 24 July 2012
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	[[Selecting NULL values.]]		[[Selecting NULL values.]]
		+
		+	<div class="summary">Summary</div>
		+
		+	<div class="progressbarbg">
		+	<div class="progressbar"></div>
		+	</div>

	<div class='extra_space' style='width:1em; height:2.5em;'></div>		<div class='extra_space' style='width:1em; height:2.5em;'></div>

← Older revision		Revision as of 00:25, 20 July 2012
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	[[Selecting NULL values.]]		[[Selecting NULL values.]]
		+
		+	<div class='extra_space' style='width:1em; height:2.5em;'></div>
		+
		+	<div class='extra_space' style='width:1em; height:2.5em;'></div>

	<h2>NULL, INNER JOIN, LEFT JOIN, RIGHT JOIN</h2>		<h2>NULL, INNER JOIN, LEFT JOIN, RIGHT JOIN</h2>

@@ Line 1: / Line 1: @@
 <div class='ref_section'>
@@ Line 80: / Line 77: @@
 </table>
 </div>
 [[Selecting NULL values.]]

@@ Line 52: / Line 52: @@
 <td align='right'>3345</td>
 <td></td>
 </tr>
 </table>
@@ Line 71: / Line 74: @@
 <td align='right'>3</td>
 <td>Engineering</td>
 </tr>
 </table>

@@ Line 3: / Line 3: @@
 Some teachers have no department.</p>
-<div class='ref_section' style='background:none'>
+<div class='ref_section'>
 <table class='zoo db_ref'>
 <caption>teacher</caption>