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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>9.1. Logical Operators</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="functions.html" title="Chapter 9. Functions and Operators" /><link rel="next" href="functions-comparison.html" title="9.2. Comparison Functions and Operators" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.1. Logical Operators</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions.html" title="Chapter 9. Functions and Operators">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-comparison.html" title="9.2. Comparison Functions and Operators">Next</a></td></tr></table><hr /></div><div class="sect1" id="FUNCTIONS-LOGICAL"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.1. Logical Operators</h2></div></div></div><a id="id-1.5.8.7.2" class="indexterm"></a><a id="id-1.5.8.7.3" class="indexterm"></a><p>
The usual logical operators are available:
<a id="id-1.5.8.7.4.1" class="indexterm"></a>
<a id="id-1.5.8.7.4.2" class="indexterm"></a>
<a id="id-1.5.8.7.4.3" class="indexterm"></a>
<a id="id-1.5.8.7.4.4" class="indexterm"></a>
<a id="id-1.5.8.7.4.5" class="indexterm"></a>
<a id="id-1.5.8.7.4.6" class="indexterm"></a>
</p><pre class="synopsis">
<code class="type">boolean</code> <code class="literal">AND</code> <code class="type">boolean</code> → <code class="returnvalue">boolean</code>
<code class="type">boolean</code> <code class="literal">OR</code> <code class="type">boolean</code> → <code class="returnvalue">boolean</code>
<code class="literal">NOT</code> <code class="type">boolean</code> → <code class="returnvalue">boolean</code>
</pre><p>
<acronym class="acronym">SQL</acronym> uses a three-valued logic system with true,
false, and <code class="literal">null</code>, which represents <span class="quote">“<span class="quote">unknown</span>”</span>.
Observe the following truth tables:
</p><div class="informaltable"><table class="informaltable" border="1"><colgroup><col /><col /><col /><col /></colgroup><thead><tr><th><em class="replaceable"><code>a</code></em></th><th><em class="replaceable"><code>b</code></em></th><th><em class="replaceable"><code>a</code></em> AND <em class="replaceable"><code>b</code></em></th><th><em class="replaceable"><code>a</code></em> OR <em class="replaceable"><code>b</code></em></th></tr></thead><tbody><tr><td>TRUE</td><td>TRUE</td><td>TRUE</td><td>TRUE</td></tr><tr><td>TRUE</td><td>FALSE</td><td>FALSE</td><td>TRUE</td></tr><tr><td>TRUE</td><td>NULL</td><td>NULL</td><td>TRUE</td></tr><tr><td>FALSE</td><td>FALSE</td><td>FALSE</td><td>FALSE</td></tr><tr><td>FALSE</td><td>NULL</td><td>FALSE</td><td>NULL</td></tr><tr><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td></tr></tbody></table></div><p>
</p><div class="informaltable"><table class="informaltable" border="1"><colgroup><col /><col /></colgroup><thead><tr><th><em class="replaceable"><code>a</code></em></th><th>NOT <em class="replaceable"><code>a</code></em></th></tr></thead><tbody><tr><td>TRUE</td><td>FALSE</td></tr><tr><td>FALSE</td><td>TRUE</td></tr><tr><td>NULL</td><td>NULL</td></tr></tbody></table></div><p>
</p><p>
The operators <code class="literal">AND</code> and <code class="literal">OR</code> are
commutative, that is, you can switch the left and right operands
without affecting the result. (However, it is not guaranteed that
the left operand is evaluated before the right operand. See <a class="xref" href="sql-expressions.html#SYNTAX-EXPRESS-EVAL" title="4.2.14. Expression Evaluation Rules">Section 4.2.14</a> for more information about the
order of evaluation of subexpressions.)
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions.html" title="Chapter 9. Functions and Operators">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-comparison.html" title="9.2. Comparison Functions and Operators">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 9. Functions and Operators </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.2. Comparison Functions and Operators</td></tr></table></div></body></html>
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