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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>43.2. Structure of PL/pgSQL</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="plpgsql-overview.html" title="43.1. Overview" /><link rel="next" href="plpgsql-declarations.html" title="43.3. Declarations" /></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">43.2. Structure of <span xmlns="http://www.w3.org/1999/xhtml" class="application">PL/pgSQL</span></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpgsql-overview.html" title="43.1. Overview">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plpgsql.html" title="Chapter 43. PL/pgSQL - SQL Procedural Language">Up</a></td><th width="60%" align="center">Chapter 43. <span xmlns="http://www.w3.org/1999/xhtml" class="application">PL/pgSQL</span> - <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym> Procedural Language</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="plpgsql-declarations.html" title="43.3. Declarations">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPGSQL-STRUCTURE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">43.2. Structure of <span class="application">PL/pgSQL</span></h2></div></div></div><p>
Functions written in <span class="application">PL/pgSQL</span> are defined
to the server by executing <a class="xref" href="sql-createfunction.html" title="CREATE FUNCTION"><span class="refentrytitle">CREATE FUNCTION</span></a> commands.
Such a command would normally look like, say,
</p><pre class="programlisting">
CREATE FUNCTION somefunc(integer, text) RETURNS integer
AS '<em class="replaceable"><code>function body text</code></em>'
LANGUAGE plpgsql;
</pre><p>
The function body is simply a string literal so far as <code class="command">CREATE
FUNCTION</code> is concerned. It is often helpful to use dollar quoting
(see <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING" title="4.1.2.4. Dollar-quoted String Constants">Section 4.1.2.4</a>) to write the function
body, rather than the normal single quote syntax. Without dollar quoting,
any single quotes or backslashes in the function body must be escaped by
doubling them. Almost all the examples in this chapter use dollar-quoted
literals for their function bodies.
</p><p>
<span class="application">PL/pgSQL</span> is a block-structured language.
The complete text of a function body must be a
<em class="firstterm">block</em>. A block is defined as:
</p><pre class="synopsis">
[<span class="optional"> <<<em class="replaceable"><code>label</code></em>>> </span>]
[<span class="optional"> DECLARE
<em class="replaceable"><code>declarations</code></em> </span>]
BEGIN
<em class="replaceable"><code>statements</code></em>
END [<span class="optional"> <em class="replaceable"><code>label</code></em> </span>];
</pre><p>
</p><p>
Each declaration and each statement within a block is terminated
by a semicolon. A block that appears within another block must
have a semicolon after <code class="literal">END</code>, as shown above;
however the final <code class="literal">END</code> that
concludes a function body does not require a semicolon.
</p><div class="tip"><h3 class="title">Tip</h3><p>
A common mistake is to write a semicolon immediately after
<code class="literal">BEGIN</code>. This is incorrect and will result in a syntax error.
</p></div><p>
A <em class="replaceable"><code>label</code></em> is only needed if you want to
identify the block for use
in an <code class="literal">EXIT</code> statement, or to qualify the names of the
variables declared in the block. If a label is given after
<code class="literal">END</code>, it must match the label at the block's beginning.
</p><p>
All key words are case-insensitive.
Identifiers are implicitly converted to lower case
unless double-quoted, just as they are in ordinary SQL commands.
</p><p>
Comments work the same way in <span class="application">PL/pgSQL</span> code as in
ordinary SQL. A double dash (<code class="literal">--</code>) starts a comment
that extends to the end of the line. A <code class="literal">/*</code> starts a
block comment that extends to the matching occurrence of
<code class="literal">*/</code>. Block comments nest.
</p><p>
Any statement in the statement section of a block
can be a <em class="firstterm">subblock</em>. Subblocks can be used for
logical grouping or to localize variables to a small group
of statements. Variables declared in a subblock mask any
similarly-named variables of outer blocks for the duration
of the subblock; but you can access the outer variables anyway
if you qualify their names with their block's label. For example:
</p><pre class="programlisting">
CREATE FUNCTION somefunc() RETURNS integer AS $$
<< outerblock >>
DECLARE
quantity integer := 30;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 30
quantity := 50;
--
-- Create a subblock
--
DECLARE
quantity integer := 80;
BEGIN
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 80
RAISE NOTICE 'Outer quantity here is %', outerblock.quantity; -- Prints 50
END;
RAISE NOTICE 'Quantity here is %', quantity; -- Prints 50
RETURN quantity;
END;
$$ LANGUAGE plpgsql;
</pre><p>
</p><div class="note"><h3 class="title">Note</h3><p>
There is actually a hidden <span class="quote">“<span class="quote">outer block</span>”</span> surrounding the body
of any <span class="application">PL/pgSQL</span> function. This block provides the
declarations of the function's parameters (if any), as well as some
special variables such as <code class="literal">FOUND</code> (see
<a class="xref" href="plpgsql-statements.html#PLPGSQL-STATEMENTS-DIAGNOSTICS" title="43.5.5. Obtaining the Result Status">Section 43.5.5</a>). The outer block is
labeled with the function's name, meaning that parameters and special
variables can be qualified with the function's name.
</p></div><p>
It is important not to confuse the use of
<code class="command">BEGIN</code>/<code class="command">END</code> for grouping statements in
<span class="application">PL/pgSQL</span> with the similarly-named SQL commands
for transaction
control. <span class="application">PL/pgSQL</span>'s <code class="command">BEGIN</code>/<code class="command">END</code>
are only for grouping; they do not start or end a transaction.
See <a class="xref" href="plpgsql-transactions.html" title="43.8. Transaction Management">Section 43.8</a> for information on managing
transactions in <span class="application">PL/pgSQL</span>.
Also, a block containing an <code class="literal">EXCEPTION</code> clause effectively
forms a subtransaction that can be rolled back without affecting the
outer transaction. For more about that see <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-ERROR-TRAPPING" title="43.6.8. Trapping Errors">Section 43.6.8</a>.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpgsql-overview.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plpgsql.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpgsql-declarations.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">43.1. Overview </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 43.3. Declarations</td></tr></table></div></body></html>
