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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>36.1. The Concept</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="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C" /><link rel="next" href="ecpg-connect.html" title="36.2. Managing Database Connections" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">36.1. The Concept</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Up</a></td><th width="60%" align="center">Chapter 36. <span class="application">ECPG</span> — Embedded <acronym class="acronym">SQL</acronym> in C</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ecpg-connect.html" title="36.2. Managing Database Connections">Next</a></td></tr></table><hr /></div><div class="sect1" id="ECPG-CONCEPT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">36.1. 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 (<code class="filename">*.pgc</code>)
+   is first passed through the embedded SQL preprocessor, which converts it
+   to an ordinary C program (<code class="filename">*.c</code>), and afterwards it can be processed by a C
+   compiler.  (For details about the compiling and linking see <a class="xref" href="ecpg-process.html" title="36.10. Processing Embedded SQL Programs">Section 36.10</a>.)
+   Converted ECPG applications call functions in the libpq library
+   through the embedded SQL library (ecpglib), and communicate with
+   the PostgreSQL server using the normal frontend-backend protocol.
+  </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 can appear at the
+   global level or within a function.
+  </p><p>
+   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. Also they allow nested
+   C-style comments as per the SQL standard. The C part of the
+   program, however, follows the C standard of not accepting nested comments.
+   Embedded <acronym class="acronym">SQL</acronym> statements likewise use SQL rules, not
+   C rules, for parsing quoted strings and identifiers.
+   (See <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS" title="4.1.2.1. String Constants">Section 4.1.2.1</a> and
+   <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS" title="4.1.1. Identifiers and Key Words">Section 4.1.1</a> respectively.  Note that
+   ECPG assumes that <code class="varname">standard_conforming_strings</code>
+   is <code class="literal">on</code>.)
+   Of course, the C part of the program follows C quoting rules.
+  </p><p>
+   The following sections explain all the embedded SQL statements.
+  </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ecpg-connect.html" title="36.2. Managing Database Connections">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 36. <span class="application">ECPG</span> — Embedded <acronym class="acronym">SQL</acronym> in C </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 36.2. Managing Database Connections</td></tr></table></div></body></html>
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