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- 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="35.10. Processing Embedded SQL Programs">Section 35.10</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. 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 that are part of the SQL standard. The C part of the
- program, however, follows the C standard of not accepting nested comments.
- </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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ecpg.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ecpg-connect.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 35. <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">Home</a></td><td width="40%" align="right" valign="top"> 35.2. Managing Database Connections</td></tr></table></div></body></html>
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