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POMySQL “WHERE IN” produces proper result but “WHERE NOT IN” does not
 

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  1. POMySQL “WHERE IN” produces proper result but “WHERE NOT IN” does not
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    <p>This is the table structure</p> <pre><code>CREATE TABLE `student_classlists` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `SessionCode` int(5) DEFAULT NULL, `CourseCode` varchar(10) DEFAULT NULL, `SectionCode` varchar(1) DEFAULT NULL, `LastName` varchar(255) DEFAULT NULL, `FirstName` varchar(255) DEFAULT NULL, `StudentId` int(10) unsigned DEFAULT NULL, `FinalGradeSIS` int(10) DEFAULT NULL, `Status` varchar(10) DEFAULT NULL, `Faculty` varchar(255) DEFAULT '', `Email` varchar(255) DEFAULT NULL, `ClassListDate` date DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=576 DEFAULT CHARSET=utf8; </code></pre> <p>The <code>Status</code> column is largely composed of <code>NULL</code> rows, with just a few exceptions. I am trying to ignore those records that are not null. The following query does not work:</p> <pre><code>SELECT StudentId FROM student_classlists WHERE `Status` NOT IN ('Drop') GROUP BY StudentId </code></pre> <p>For some reason it produces an unexpected and empty result. But a very similar query with the only exception of dropping the <code>NOT</code> produces an expected result</p> <pre><code>SELECT StudentId FROM student_classlists WHERE `Status` IN ('Drop') GROUP BY StudentId </code></pre> <p>What's happening here?</p>
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    1. USLevi
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    1. COIt would be useful to see some of the data
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    2. COAnother victim of three-valued logic. Check out http://stackoverflow.com/questions/129077/not-in-constraint-and-null-values for the reverse.
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      1. USPaul Draper
 

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