diff options
Diffstat (limited to 'doc/src/sgml/html/ecpg-dynamic.html')
| -rw-r--r-- | doc/src/sgml/html/ecpg-dynamic.html | 103 |
1 files changed, 103 insertions, 0 deletions
diff --git a/doc/src/sgml/html/ecpg-dynamic.html b/doc/src/sgml/html/ecpg-dynamic.html new file mode 100644 index 0000000..4ca4625 --- /dev/null +++ b/doc/src/sgml/html/ecpg-dynamic.html @@ -0,0 +1,103 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!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>36.5. Dynamic SQL</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-variables.html" title="36.4. Using Host Variables" /><link rel="next" href="ecpg-pgtypes.html" title="36.6. pgtypes Library" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">36.5. Dynamic SQL</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ecpg-variables.html" title="36.4. Using Host Variables">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 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ecpg-pgtypes.html" title="36.6. pgtypes Library">Next</a></td></tr></table><hr /></div><div class="sect1" id="ECPG-DYNAMIC"><div class="titlepage"><div><div><h2 class="title" style="clear: both">36.5. Dynamic SQL <a href="#ECPG-DYNAMIC" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="ecpg-dynamic.html#ECPG-DYNAMIC-WITHOUT-RESULT">36.5.1. Executing Statements without a Result Set</a></span></dt><dt><span class="sect2"><a href="ecpg-dynamic.html#ECPG-DYNAMIC-INPUT">36.5.2. Executing a Statement with Input Parameters</a></span></dt><dt><span class="sect2"><a href="ecpg-dynamic.html#ECPG-DYNAMIC-WITH-RESULT">36.5.3. Executing a Statement with a Result Set</a></span></dt></dl></div><p> + In many cases, the particular SQL statements that an application + has to execute are known at the time the application is written. + In some cases, however, the SQL statements are composed at run time + or provided by an external source. In these cases you cannot embed + the SQL statements directly into the C source code, but there is a + facility that allows you to call arbitrary SQL statements that you + provide in a string variable. + </p><div class="sect2" id="ECPG-DYNAMIC-WITHOUT-RESULT"><div class="titlepage"><div><div><h3 class="title">36.5.1. Executing Statements without a Result Set <a href="#ECPG-DYNAMIC-WITHOUT-RESULT" class="id_link">#</a></h3></div></div></div><p> + The simplest way to execute an arbitrary SQL statement is to use + the command <code class="command">EXECUTE IMMEDIATE</code>. For example: +</p><pre class="programlisting"> +EXEC SQL BEGIN DECLARE SECTION; +const char *stmt = "CREATE TABLE test1 (...);"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL EXECUTE IMMEDIATE :stmt; +</pre><p> + <code class="command">EXECUTE IMMEDIATE</code> can be used for SQL + statements that do not return a result set (e.g., + DDL, <code class="command">INSERT</code>, <code class="command">UPDATE</code>, + <code class="command">DELETE</code>). You cannot execute statements that + retrieve data (e.g., <code class="command">SELECT</code>) this way. The + next section describes how to do that. + </p></div><div class="sect2" id="ECPG-DYNAMIC-INPUT"><div class="titlepage"><div><div><h3 class="title">36.5.2. Executing a Statement with Input Parameters <a href="#ECPG-DYNAMIC-INPUT" class="id_link">#</a></h3></div></div></div><p> + A more powerful way to execute arbitrary SQL statements is to + prepare them once and execute the prepared statement as often as + you like. It is also possible to prepare a generalized version of + a statement and then execute specific versions of it by + substituting parameters. When preparing the statement, write + question marks where you want to substitute parameters later. For + example: +</p><pre class="programlisting"> +EXEC SQL BEGIN DECLARE SECTION; +const char *stmt = "INSERT INTO test1 VALUES(?, ?);"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL PREPARE mystmt FROM :stmt; + ... +EXEC SQL EXECUTE mystmt USING 42, 'foobar'; +</pre><p> + </p><p> + When you don't need the prepared statement anymore, you should + deallocate it: +</p><pre class="programlisting"> +EXEC SQL DEALLOCATE PREPARE <em class="replaceable"><code>name</code></em>; +</pre><p> + </p></div><div class="sect2" id="ECPG-DYNAMIC-WITH-RESULT"><div class="titlepage"><div><div><h3 class="title">36.5.3. Executing a Statement with a Result Set <a href="#ECPG-DYNAMIC-WITH-RESULT" class="id_link">#</a></h3></div></div></div><p> + To execute an SQL statement with a single result row, + <code class="command">EXECUTE</code> can be used. To save the result, add + an <code class="literal">INTO</code> clause. +</p><pre class="programlisting"> +EXEC SQL BEGIN DECLARE SECTION; +const char *stmt = "SELECT a, b, c FROM test1 WHERE a > ?"; +int v1, v2; +VARCHAR v3[50]; +EXEC SQL END DECLARE SECTION; + +EXEC SQL PREPARE mystmt FROM :stmt; + ... +EXEC SQL EXECUTE mystmt INTO :v1, :v2, :v3 USING 37; + +</pre><p> + An <code class="command">EXECUTE</code> command can have an + <code class="literal">INTO</code> clause, a <code class="literal">USING</code> clause, + both, or neither. + </p><p> + If a query is expected to return more than one result row, a + cursor should be used, as in the following example. + (See <a class="xref" href="ecpg-commands.html#ECPG-CURSORS" title="36.3.2. Using Cursors">Section 36.3.2</a> for more details about the + cursor.) +</p><pre class="programlisting"> +EXEC SQL BEGIN DECLARE SECTION; +char dbaname[128]; +char datname[128]; +char *stmt = "SELECT u.usename as dbaname, d.datname " + " FROM pg_database d, pg_user u " + " WHERE d.datdba = u.usesysid"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL CONNECT TO testdb AS con1 USER testuser; +EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + +EXEC SQL PREPARE stmt1 FROM :stmt; + +EXEC SQL DECLARE cursor1 CURSOR FOR stmt1; +EXEC SQL OPEN cursor1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + EXEC SQL FETCH cursor1 INTO :dbaname,:datname; + printf("dbaname=%s, datname=%s\n", dbaname, datname); +} + +EXEC SQL CLOSE cursor1; + +EXEC SQL COMMIT; +EXEC SQL DISCONNECT ALL; +</pre><p> + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ecpg-variables.html" title="36.4. Using Host Variables">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-pgtypes.html" title="36.6. pgtypes Library">Next</a></td></tr><tr><td width="40%" align="left" valign="top">36.4. Using Host Variables </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 36.6. pgtypes Library</td></tr></table></div></body></html>
\ No newline at end of file |