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add sqlite 3.3.8 to in tree libs
git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@3735 d0543943-73ff-0310-b7d9-9358b9ac24b2
This commit is contained in:
Michael Jerris
329
libs/sqlite/www/nulls.tcl
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329
libs/sqlite/www/nulls.tcl
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@@ -0,0 +1,329 @@
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#
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# Run this script to generated a nulls.html output file
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#
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set rcsid {$Id: nulls.tcl,v 1.8 2004/10/10 17:24:55 drh Exp $}
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source common.tcl
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header {NULL Handling in SQLite}
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puts {
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<h2>NULL Handling in SQLite Versus Other Database Engines</h2>
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<p>
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The goal is
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to make SQLite handle NULLs in a standards-compliant way.
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But the descriptions in the SQL standards on how to handle
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NULLs seem ambiguous.
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It is not clear from the standards documents exactly how NULLs should
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be handled in all circumstances.
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</p>
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<p>
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So instead of going by the standards documents, various popular
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SQL engines were tested to see how they handle NULLs. The idea
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was to make SQLite work like all the other engines.
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A SQL test script was developed and run by volunteers on various
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SQL RDBMSes and the results of those tests were used to deduce
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how each engine processed NULL values.
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The original tests were run in May of 2002.
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A copy of the test script is found at the end of this document.
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</p>
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<p>
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SQLite was originally coded in such a way that the answer to
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all questions in the chart below would be "Yes". But the
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experiments run on other SQL engines showed that none of them
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worked this way. So SQLite was modified to work the same as
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Oracle, PostgreSQL, and DB2. This involved making NULLs
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indistinct for the purposes of the SELECT DISTINCT statement and
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for the UNION operator in a SELECT. NULLs are still distinct
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in a UNIQUE column. This seems somewhat arbitrary, but the desire
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to be compatible with other engines outweighted that objection.
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</p>
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<p>
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It is possible to make SQLite treat NULLs as distinct for the
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purposes of the SELECT DISTINCT and UNION. To do so, one should
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change the value of the NULL_ALWAYS_DISTINCT #define in the
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<tt>sqliteInt.h</tt> source file and recompile.
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</p>
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<blockquote>
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<p>
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<i>Update 2003-07-13:</i>
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Since this document was originally written some of the database engines
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tested have been updated and users have been kind enough to send in
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corrections to the chart below. The original data showed a wide variety
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of behaviors, but over time the range of behaviors has converged toward
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the PostgreSQL/Oracle model. The only significant difference
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is that Informix and MS-SQL both threat NULLs as
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indistinct in a UNIQUE column.
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</p>
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<p>
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The fact that NULLs are distinct for UNIQUE columns but are indistinct for
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SELECT DISTINCT and UNION continues to be puzzling. It seems that NULLs
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should be either distinct everywhere or nowhere. And the SQL standards
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documents suggest that NULLs should be distinct everywhere. Yet as of
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this writing, no SQL engine tested treats NULLs as distinct in a SELECT
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DISTINCT statement or in a UNION.
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</p>
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</blockquote>
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<p>
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The following table shows the results of the NULL handling experiments.
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</p>
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<table border=1 cellpadding=3 width="100%">
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<tr><th>  </th>
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<th>SQLite</th>
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<th>PostgreSQL</th>
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<th>Oracle</th>
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<th>Informix</th>
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<th>DB2</th>
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<th>MS-SQL</th>
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<th>OCELOT</th>
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</tr>
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<tr><td>Adding anything to null gives null</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>Multiplying null by zero gives null</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>nulls are distinct in a UNIQUE column</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#aaaad2">(Note 4)</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>nulls are distinct in SELECT DISTINCT</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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</tr>
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<tr><td>nulls are distinct in a UNION</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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</tr>
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<tr><td>"CASE WHEN null THEN 1 ELSE 0 END" is 0?</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>"null OR true" is true</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>"not (null AND false)" is true</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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</table>
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<table border=1 cellpadding=3 width="100%">
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<tr><th>  </th>
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<th>MySQL<br>3.23.41</th>
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<th>MySQL<br>4.0.16</th>
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<th>Firebird</th>
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<th>SQL<br>Anywhere</th>
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<th>Borland<br>Interbase</th>
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</tr>
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<tr><td>Adding anything to null gives null</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>Multiplying null by zero gives null</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>nulls are distinct in a UNIQUE column</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#aaaad2">(Note 4)</td>
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<td valign="center" align="center" bgcolor="#aaaad2">(Note 4)</td>
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</tr>
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<tr><td>nulls are distinct in SELECT DISTINCT</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No (Note 1)</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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</tr>
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<tr><td>nulls are distinct in a UNION</td>
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<td valign="center" align="center" bgcolor="#aaaad2">(Note 3)</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No (Note 1)</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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</tr>
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<tr><td>"CASE WHEN null THEN 1 ELSE 0 END" is 0?</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#aaaad2">(Note 5)</td>
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</tr>
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<tr><td>"null OR true" is true</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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<tr><td>"not (null AND false)" is true</td>
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<td valign="center" align="center" bgcolor="#c7a9a9">No</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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<td valign="center" align="center" bgcolor="#a9c7a9">Yes</td>
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</tr>
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</table>
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<table border=0 align="right" cellpadding=0 cellspacing=0>
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<tr>
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<td valign="top" rowspan=5>Notes: </td>
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<td>1. </td>
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<td>Older versions of firebird omits all NULLs from SELECT DISTINCT
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and from UNION.</td>
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</tr>
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<tr><td>2. </td>
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<td>Test data unavailable.</td>
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</tr>
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<tr><td>3. </td>
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<td>MySQL version 3.23.41 does not support UNION.</td>
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</tr>
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<tr><td>4. </td>
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<td>DB2, SQL Anywhere, and Borland Interbase
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do not allow NULLs in a UNIQUE column.</td>
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</tr>
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<tr><td>5. </td>
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<td>Borland Interbase does not support CASE expressions.</td>
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</tr>
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</table>
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<br clear="both">
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<p> </p>
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<p>
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The following script was used to gather information for the table
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above.
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</p>
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<pre>
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-- I have about decided that SQL's treatment of NULLs is capricious and cannot be
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-- deduced by logic. It must be discovered by experiment. To that end, I have
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-- prepared the following script to test how various SQL databases deal with NULL.
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-- My aim is to use the information gather from this script to make SQLite as much
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-- like other databases as possible.
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--
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-- If you could please run this script in your database engine and mail the results
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-- to me at drh@hwaci.com, that will be a big help. Please be sure to identify the
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-- database engine you use for this test. Thanks.
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--
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-- If you have to change anything to get this script to run with your database
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-- engine, please send your revised script together with your results.
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--
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-- Create a test table with data
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create table t1(a int, b int, c int);
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insert into t1 values(1,0,0);
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insert into t1 values(2,0,1);
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insert into t1 values(3,1,0);
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insert into t1 values(4,1,1);
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insert into t1 values(5,null,0);
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insert into t1 values(6,null,1);
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insert into t1 values(7,null,null);
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-- Check to see what CASE does with NULLs in its test expressions
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select a, case when b<>0 then 1 else 0 end from t1;
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select a+10, case when not b<>0 then 1 else 0 end from t1;
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select a+20, case when b<>0 and c<>0 then 1 else 0 end from t1;
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select a+30, case when not (b<>0 and c<>0) then 1 else 0 end from t1;
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select a+40, case when b<>0 or c<>0 then 1 else 0 end from t1;
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select a+50, case when not (b<>0 or c<>0) then 1 else 0 end from t1;
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select a+60, case b when c then 1 else 0 end from t1;
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select a+70, case c when b then 1 else 0 end from t1;
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-- What happens when you multiple a NULL by zero?
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select a+80, b*0 from t1;
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select a+90, b*c from t1;
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-- What happens to NULL for other operators?
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select a+100, b+c from t1;
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-- Test the treatment of aggregate operators
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select count(*), count(b), sum(b), avg(b), min(b), max(b) from t1;
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-- Check the behavior of NULLs in WHERE clauses
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select a+110 from t1 where b<10;
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select a+120 from t1 where not b>10;
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select a+130 from t1 where b<10 OR c=1;
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select a+140 from t1 where b<10 AND c=1;
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select a+150 from t1 where not (b<10 AND c=1);
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select a+160 from t1 where not (c=1 AND b<10);
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-- Check the behavior of NULLs in a DISTINCT query
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select distinct b from t1;
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-- Check the behavior of NULLs in a UNION query
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select b from t1 union select b from t1;
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-- Create a new table with a unique column. Check to see if NULLs are considered
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-- to be distinct.
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create table t2(a int, b int unique);
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insert into t2 values(1,1);
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insert into t2 values(2,null);
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insert into t2 values(3,null);
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select * from t2;
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drop table t1;
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drop table t2;
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</pre>
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}
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footer $rcsid
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Reference in New Issue
Block a user