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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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<title>6.1. Logical Operators — Presto 0.206 Documentation</title>
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<h1 class="heading"><a href="../index.html">
<span>Presto 0.206 Documentation</span></a></h1>
<h2 class="heading"><span>6.1. Logical Operators</span></h2>
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<div class="section" id="logical-operators">
<h1>6.1. Logical Operators</h1>
<div class="section" id="id1">
<h2>Logical Operators</h2>
<table border="1" class="docutils">
<colgroup>
<col width="19%" />
<col width="65%" />
<col width="16%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Operator</th>
<th class="head">Description</th>
<th class="head">Example</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal"><span class="pre">AND</span></code></td>
<td>True if both values are true</td>
<td>a AND b</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">OR</span></code></td>
<td>True if either value is true</td>
<td>a OR b</td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">NOT</span></code></td>
<td>True if the value is false</td>
<td>NOT a</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="effect-of-null-on-logical-operators">
<h2>Effect of NULL on Logical Operators</h2>
<p>The result of an <code class="docutils literal"><span class="pre">AND</span></code> comparison may be <code class="docutils literal"><span class="pre">NULL</span></code> if one or both
sides of the expression are <code class="docutils literal"><span class="pre">NULL</span></code>. If at least one side of an
<code class="docutils literal"><span class="pre">AND</span></code> operator is <code class="docutils literal"><span class="pre">FALSE</span></code> the expression evaluates to <code class="docutils literal"><span class="pre">FALSE</span></code>:</p>
<div class="highlight-sql"><div class="highlight"><pre><span></span><span class="k">SELECT</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">)</span> <span class="k">AND</span> <span class="k">true</span><span class="p">;</span> <span class="c1">-- null</span>
<span class="k">SELECT</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">)</span> <span class="k">AND</span> <span class="k">false</span><span class="p">;</span> <span class="c1">-- false</span>
<span class="k">SELECT</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">)</span> <span class="k">AND</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">);</span> <span class="c1">-- null</span>
</pre></div>
</div>
<p>The result of an <code class="docutils literal"><span class="pre">OR</span></code> comparison may be <code class="docutils literal"><span class="pre">NULL</span></code> if one or both
sides of the expression are <code class="docutils literal"><span class="pre">NULL</span></code>. If at least one side of an
<code class="docutils literal"><span class="pre">OR</span></code> operator is <code class="docutils literal"><span class="pre">TRUE</span></code> the expression evaluates to <code class="docutils literal"><span class="pre">TRUE</span></code>:</p>
<div class="highlight-sql"><div class="highlight"><pre><span></span><span class="k">SELECT</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">)</span> <span class="k">OR</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">);</span> <span class="c1">-- null</span>
<span class="k">SELECT</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">)</span> <span class="k">OR</span> <span class="k">false</span><span class="p">;</span> <span class="c1">-- null</span>
<span class="k">SELECT</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">)</span> <span class="k">OR</span> <span class="k">true</span><span class="p">;</span> <span class="c1">-- true</span>
</pre></div>
</div>
<p>The following truth table demonstrates the handling of
<code class="docutils literal"><span class="pre">NULL</span></code> in <code class="docutils literal"><span class="pre">AND</span></code> and <code class="docutils literal"><span class="pre">OR</span></code>:</p>
<table border="1" class="docutils">
<colgroup>
<col width="25%" />
<col width="25%" />
<col width="25%" />
<col width="25%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">a</th>
<th class="head">b</th>
<th class="head">a AND b</th>
<th class="head">a OR b</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
</tr>
</tbody>
</table>
<p>The logical complement of <code class="docutils literal"><span class="pre">NULL</span></code> is <code class="docutils literal"><span class="pre">NULL</span></code> as shown in the following example:</p>
<div class="highlight-sql"><div class="highlight"><pre><span></span><span class="k">SELECT</span> <span class="k">NOT</span> <span class="k">CAST</span><span class="p">(</span><span class="k">null</span> <span class="k">AS</span> <span class="nb">boolean</span><span class="p">);</span> <span class="c1">-- null</span>
</pre></div>
</div>
<p>The following truth table demonstrates the handling of <code class="docutils literal"><span class="pre">NULL</span></code> in <code class="docutils literal"><span class="pre">NOT</span></code>:</p>
<table border="1" class="docutils">
<colgroup>
<col width="50%" />
<col width="50%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">a</th>
<th class="head">NOT a</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
<td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">FALSE</span></code></td>
<td><code class="docutils literal"><span class="pre">TRUE</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">NULL</span></code></td>
<td><code class="docutils literal"><span class="pre">NULL</span></code></td>
</tr>
</tbody>
</table>
</div>
</div>
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