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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>37.14. 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 V1.79.1" /><link rel="prev" href="xtypes.html" title="37.13. User-Defined Types" /><link rel="next" href="xoper-optimization.html" title="37.15. 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">37.14. User-Defined Operators</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="xtypes.html" title="37.13. User-Defined Types">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="extend.html" title="Chapter 37. Extending SQL">Up</a></td><th width="60%" align="center">Chapter 37. 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 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="xoper-optimization.html" title="37.15. 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">37.14. User-Defined Operators</h2></div></div></div><a id="id-1.8.3.17.2" 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-1.8.3.17.4.2" 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="37.13. User-Defined Types">Section 37.13</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">37.13. 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"> 37.15. Operator Optimization Information</td></tr></table></div></body></html>
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