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<title>32.3.User-Defined Functions</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="xfunc"></a>32.3.User-Defined Functions</h2></div></div></div>
<a name="id703966"></a><p> <span class="productname">PostgreSQL</span> provides four kinds of
functions:
</p>
<div class="itemizedlist"><ul type="disc">
<li><p> query language functions (functions written in
<acronym class="acronym">SQL</acronym>) (<a href="xfunc-sql.html" title="32.4.Query Language (SQL) Functions">Section32.4, “Query Language (<acronym class="acronym">SQL</acronym>) Functions”</a>)
</p></li>
<li><p> procedural language functions (functions written in, for
example, <span class="application">PL/pgSQL</span> or <span class="application">PL/Tcl</span>)
(<a href="xfunc-pl.html" title="32.7.Procedural Language Functions">Section32.7, “Procedural Language Functions”</a>)
</p></li>
<li><p> internal functions (<a href="xfunc-internal.html" title="32.8.Internal Functions">Section32.8, “Internal Functions”</a>)
</p></li>
<li><p> C-language functions (<a href="xfunc-c.html" title="32.9.C-Language Functions">Section32.9, “C-Language Functions”</a>)
</p></li>
</ul></div>
<p>
</p>
<p> Every kind
of function can take base types, composite types, or
combinations of these as arguments (parameters). In addition,
every kind of function can return a base type or
a composite type. Functions may also be defined to return
sets of base or composite values.
</p>
<p> Many kinds of functions can take or return certain pseudo-types
(such as polymorphic types), but the available facilities vary.
Consult the description of each kind of function for more details.
</p>
<p> It's easiest to define <acronym class="acronym">SQL</acronym>
functions, so we'll start by discussing those.
Most of the concepts presented for <acronym class="acronym">SQL</acronym> functions
will carry over to the other types of functions.
</p>
<p> Throughout this chapter, it can be useful to look at the reference
page of the <a href="sql-createfunction.html">CREATE FUNCTION</a> command to
understand the examples better. Some examples from this chapter
can be found in <code class="filename">funcs.sql</code> and
<code class="filename">funcs.c</code> in the <code class="filename">src/tutorial</code>
directory in the <span class="productname">PostgreSQL</span> source
distribution.
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