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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>38.13. User-defined 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="xtypes.html" title="38.12. User-defined Types" /><link rel="next" href="xoper-optimization.html" title="38.14. Operator Optimization Information" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">38.13. User-defined Operators</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="xtypes.html" title="38.12. User-defined Types">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="extend.html" title="Chapter 38. Extending SQL">Up</a></td><th width="60%" align="center">Chapter 38. Extending <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym></th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="xoper-optimization.html" title="38.14. Operator Optimization Information">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="XOPER"><div class="titlepage"><div><div><h2 class="title" style="clear: both">38.13. User-defined Operators</h2></div></div></div><a id="id-1.8.3.16.2" class="indexterm"></a><p>
Every operator is <span class="quote">“<span class="quote">syntactic sugar</span>”</span> for a call to an
underlying function that does the real work; so you must
first create the underlying function before you can create
the operator. However, an operator is <span class="emphasis"><em>not merely</em></span>
syntactic sugar, because it carries additional information
that helps the query planner optimize queries that use the
operator. The next section will be devoted to explaining
that additional information.
</p><p>
<span class="productname">PostgreSQL</span> supports left unary, right
unary, and binary operators. Operators can be
overloaded;<a id="id-1.8.3.16.4.2" class="indexterm"></a>
that is, the same operator name can be used for different operators
that have different numbers and types of operands. When a query is
executed, the system determines the operator to call from the
number and types of the provided operands.
</p><p>
Here is an example of creating an operator for adding two complex
numbers. We assume we've already created the definition of type
<code class="type">complex</code> (see <a class="xref" href="xtypes.html" title="38.12. User-defined Types">Section 38.12</a>). First we need a
function that does the work, then we can define the operator:
</p><pre class="programlisting">
CREATE FUNCTION complex_add(complex, complex)
RETURNS complex
AS '<em class="replaceable"><code>filename</code></em>', 'complex_add'
LANGUAGE C IMMUTABLE STRICT;
CREATE OPERATOR + (
leftarg = complex,
rightarg = complex,
function = complex_add,
commutator = +
);
</pre><p>
</p><p>
Now we could execute a query like this:
</p><pre class="screen">
SELECT (a + b) AS c FROM test_complex;
c
-----------------
(5.2,6.05)
(133.42,144.95)
</pre><p>
</p><p>
We've shown how to create a binary operator here. To create unary
operators, just omit one of <code class="literal">leftarg</code> (for left unary) or
<code class="literal">rightarg</code> (for right unary). The <code class="literal">function</code>
clause and the argument clauses are the only required items in
<code class="command">CREATE OPERATOR</code>. The <code class="literal">commutator</code>
clause shown in the example is an optional hint to the query
optimizer. Further details about <code class="literal">commutator</code> and other
optimizer hints appear in the next section.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="xtypes.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extend.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="xoper-optimization.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">38.12. User-defined Types </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 38.14. Operator Optimization Information</td></tr></table></div></body></html>
