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<title>Chapter30.ECPG - Embedded SQL in C</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" lang="en" id="ecpg">
<div class="titlepage"><div><div><h2 class="title">
<a name="ecpg"></a>Chapter30.<span class="application">ECPG</span> - Embedded <acronym class="acronym">SQL</acronym> in C</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="ecpg.html#ecpg-concept">30.1. The Concept</a></span></dt>
<dt><span class="sect1"><a href="ecpg-connect.html">30.2. Connecting to the Database Server</a></span></dt>
<dt><span class="sect1"><a href="ecpg-disconnect.html">30.3. Closing a Connection</a></span></dt>
<dt><span class="sect1"><a href="ecpg-commands.html">30.4. Running SQL Commands</a></span></dt>
<dt><span class="sect1"><a href="ecpg-set-connection.html">30.5. Choosing a Connection</a></span></dt>
<dt><span class="sect1"><a href="ecpg-variables.html">30.6. Using Host Variables</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="ecpg-variables.html#id689929">30.6.1. Overview</a></span></dt>
<dt><span class="sect2"><a href="ecpg-variables.html#id689971">30.6.2. Declare Sections</a></span></dt>
<dt><span class="sect2"><a href="ecpg-variables.html#id690062">30.6.3. <code class="command">SELECT INTO</code> and <code class="command">FETCH INTO</code></a></span></dt>
<dt><span class="sect2"><a href="ecpg-variables.html#id690170">30.6.4. Indicators</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="ecpg-dynamic.html">30.7. Dynamic SQL</a></span></dt>
<dt><span class="sect1"><a href="ecpg-descriptors.html">30.8. Using SQL Descriptor Areas</a></span></dt>
<dt><span class="sect1"><a href="ecpg-errors.html">30.9. Error Handling</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="ecpg-errors.html#id690723">30.9.1. Setting Callbacks</a></span></dt>
<dt><span class="sect2"><a href="ecpg-errors.html#id691022">30.9.2. sqlca</a></span></dt>
<dt><span class="sect2"><a href="ecpg-errors.html#id691292">30.9.3. <code class="literal">SQLSTATE</code> vs <code class="literal">SQLCODE</code></a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="ecpg-include.html">30.10. Including Files</a></span></dt>
<dt><span class="sect1"><a href="ecpg-process.html">30.11. Processing Embedded SQL Programs</a></span></dt>
<dt><span class="sect1"><a href="ecpg-library.html">30.12. Library Functions</a></span></dt>
<dt><span class="sect1"><a href="ecpg-develop.html">30.13. Internals</a></span></dt>
</dl>
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<a name="id689212"></a><a name="id689026"></a><a name="id689036"></a><p> This chapter describes the embedded <acronym class="acronym">SQL</acronym> package
for <span class="productname">PostgreSQL</span>. It was written by
Linus Tolke (<code class="email"><<a href="mailto:linus@epact.se">linus@epact.se</a>></code>) and Michael Meskes
(<code class="email"><<a href="mailto:meskes@postgresql.org">meskes@postgresql.org</a>></code>). Originally it was written to work with
<acronym class="acronym">C</acronym>. It also works with <acronym class="acronym">C++</acronym>, but
it does not recognize all <acronym class="acronym">C++</acronym> constructs yet.
</p>
<p> This documentation is quite incomplete. But since this
interface is standardized, additional information can be found in
many resources about SQL.
</p>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="ecpg-concept"></a>30.1.The Concept</h2></div></div></div>
<p> An embedded SQL program consists of code written in an ordinary
programming language, in this case C, mixed with SQL commands in
specially marked sections. To build the program, the source code
is first passed through the embedded SQL preprocessor, which converts it
to an ordinary C program, and afterwards it can be processed by a C
compiler.
</p>
<p> Embedded <acronym class="acronym">SQL</acronym> has advantages over other methods
for handling <acronym class="acronym">SQL</acronym> commands from C code. First, it
takes care of the tedious passing of information to and from
variables in your <acronym class="acronym">C</acronym> program. Second, the SQL
code in the program is checked at build time for syntactical
correctness. Third, embedded <acronym class="acronym">SQL</acronym> in C is
specified in the <acronym class="acronym">SQL</acronym> standard and supported by
many other <acronym class="acronym">SQL</acronym> database systems. The
<span class="productname">PostgreSQL</span> implementation is designed to match this
standard as much as possible, and it is usually possible to port
embedded <acronym class="acronym">SQL</acronym> programs written for other SQL
databases to <span class="productname">PostgreSQL</span> with relative
ease.
</p>
<p> As already stated, programs written for the embedded
<acronym class="acronym">SQL</acronym> interface are normal C programs with special
code inserted to perform database-related actions. This special
code always has the form
</p>
<pre class="programlisting">EXEC SQL ...;</pre>
<p>
These statements syntactically take the place of a C statement.
Depending on the particular statement, they may appear at the
global level or within a function. Embedded
<acronym class="acronym">SQL</acronym> statements follow the case-sensitivity rules
of normal <acronym class="acronym">SQL</acronym> code, and not those of C.
</p>
<p> The following sections explain all the embedded SQL statements.
</p>
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