codekingpro/portable-devtools

1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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>GET DESCRIPTOR</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-sql-execute-immediate.html" title="EXECUTE IMMEDIATE" /><link rel="next" href="ecpg-sql-open.html" title="OPEN" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">GET DESCRIPTOR</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ecpg-sql-execute-immediate.html" title="EXECUTE IMMEDIATE">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="ecpg-sql-commands.html" title="36.14. Embedded SQL Commands">Up</a></td><th width="60%" align="center">36.14. Embedded SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ecpg-sql-open.html" title="OPEN">Next</a></td></tr></table><hr /></div><div class="refentry" id="ECPG-SQL-GET-DESCRIPTOR"><div class="titlepage"></div><div class="refnamediv"><h2>GET DESCRIPTOR</h2><p>GET DESCRIPTOR — get information from an SQL descriptor area</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">3GET DESCRIPTOR <em class="replaceable"><code>descriptor_name</code></em> <em class="replaceable"><code>:cvariable</code></em> = <em class="replaceable"><code>descriptor_header_item</code></em> [, ... ]4GET DESCRIPTOR <em class="replaceable"><code>descriptor_name</code></em> VALUE <em class="replaceable"><code>column_number</code></em> <em class="replaceable"><code>:cvariable</code></em> = <em class="replaceable"><code>descriptor_item</code></em> [, ... ]5</pre></div><div class="refsect1" id="id-1.7.5.20.11.3"><h2>Description</h2><p>6     <code class="command">GET DESCRIPTOR</code> retrieves information about a7     query result set from an SQL descriptor area and stores it into8     host variables.  A descriptor area is typically populated9     using <code class="command">FETCH</code> or <code class="command">SELECT</code>10     before using this command to transfer the information into host11     language variables.12    </p><p>13     This command has two forms: The first form retrieves14     descriptor <span class="quote">“<span class="quote">header</span>”</span> items, which apply to the result15     set in its entirety.  One example is the row count.  The second16     form, which requires the column number as additional parameter,17     retrieves information about a particular column.  Examples are18     the column name and the actual column value.19    </p></div><div class="refsect1" id="id-1.7.5.20.11.4"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt id="ECPG-SQL-GET-DESCRIPTOR-DESCRIPTOR-NAME"><span class="term"><em class="replaceable"><code>descriptor_name</code></em></span> <a href="#ECPG-SQL-GET-DESCRIPTOR-DESCRIPTOR-NAME" class="id_link">#</a></dt><dd><p>20        A descriptor name.21       </p></dd><dt id="ECPG-SQL-GET-DESCRIPTOR-DESCRIPTOR-HEADER-ITEM"><span class="term"><em class="replaceable"><code>descriptor_header_item</code></em></span> <a href="#ECPG-SQL-GET-DESCRIPTOR-DESCRIPTOR-HEADER-ITEM" class="id_link">#</a></dt><dd><p>22        A token identifying which header information item to retrieve.23        Only <code class="literal">COUNT</code>, to get the number of columns in the24        result set, is currently supported.25       </p></dd><dt id="ECPG-SQL-GET-DESCRIPTOR-COLUMN-NUMBER"><span class="term"><em class="replaceable"><code>column_number</code></em></span> <a href="#ECPG-SQL-GET-DESCRIPTOR-COLUMN-NUMBER" class="id_link">#</a></dt><dd><p>26        The number of the column about which information is to be27        retrieved.  The count starts at 1.28       </p></dd><dt id="ECPG-SQL-GET-DESCRIPTOR-DESCRIPTOR-ITEM"><span class="term"><em class="replaceable"><code>descriptor_item</code></em></span> <a href="#ECPG-SQL-GET-DESCRIPTOR-DESCRIPTOR-ITEM" class="id_link">#</a></dt><dd><p>29        A token identifying which item of information about a column30        to retrieve.  See <a class="xref" href="ecpg-descriptors.html#ECPG-NAMED-DESCRIPTORS" title="36.7.1. Named SQL Descriptor Areas">Section 36.7.1</a> for31        a list of supported items.32       </p></dd><dt id="ECPG-SQL-GET-DESCRIPTOR-CVARIABLE"><span class="term"><em class="replaceable"><code>cvariable</code></em></span> <a href="#ECPG-SQL-GET-DESCRIPTOR-CVARIABLE" class="id_link">#</a></dt><dd><p>33        A host variable that will receive the data retrieved from the34        descriptor area.35       </p></dd></dl></div></div><div class="refsect1" id="id-1.7.5.20.11.5"><h2>Examples</h2><p>36     An example to retrieve the number of columns in a result set:37</p><pre class="programlisting">38EXEC SQL GET DESCRIPTOR d :d_count = COUNT;39</pre><p>40    </p><p>41     An example to retrieve a data length in the first column:42</p><pre class="programlisting">43EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;44</pre><p>45    </p><p>46     An example to retrieve the data body of the second column as a47     string:48</p><pre class="programlisting">49EXEC SQL GET DESCRIPTOR d VALUE 2 :d_data = DATA;50</pre><p>51    </p><p>52     Here is an example for a whole procedure of53     executing <code class="literal">SELECT current_database();</code> and showing the number of54     columns, the column data length, and the column data:55</p><pre class="programlisting">56int57main(void)58{59EXEC SQL BEGIN DECLARE SECTION;60    int  d_count;61    char d_data[1024];62    int  d_returned_octet_length;63EXEC SQL END DECLARE SECTION;64 65    EXEC SQL CONNECT TO testdb AS con1 USER testuser;66    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;67    EXEC SQL ALLOCATE DESCRIPTOR d;68 69    /* Declare, open a cursor, and assign a descriptor to the cursor  */70    EXEC SQL DECLARE cur CURSOR FOR SELECT current_database();71    EXEC SQL OPEN cur;72    EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d;73 74    /* Get a number of total columns */75    EXEC SQL GET DESCRIPTOR d :d_count = COUNT;76    printf("d_count                 = %d\n", d_count);77 78    /* Get length of a returned column */79    EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;80    printf("d_returned_octet_length = %d\n", d_returned_octet_length);81 82    /* Fetch the returned column as a string */83    EXEC SQL GET DESCRIPTOR d VALUE 1 :d_data = DATA;84    printf("d_data                  = %s\n", d_data);85 86    /* Closing */87    EXEC SQL CLOSE cur;88    EXEC SQL COMMIT;89 90    EXEC SQL DEALLOCATE DESCRIPTOR d;91    EXEC SQL DISCONNECT ALL;92 93    return 0;94}95</pre><p>96     When the example is executed, the result will look like this:97</p><pre class="screen">98d_count                 = 199d_returned_octet_length = 6100d_data                  = testdb101</pre><p>102    </p></div><div class="refsect1" id="id-1.7.5.20.11.6"><h2>Compatibility</h2><p>103     <code class="command">GET DESCRIPTOR</code> is specified in the SQL standard.104    </p></div><div class="refsect1" id="id-1.7.5.20.11.7"><h2>See Also</h2><span class="simplelist"><a class="xref" href="ecpg-sql-allocate-descriptor.html" title="ALLOCATE DESCRIPTOR">ALLOCATE DESCRIPTOR</a>, <a class="xref" href="ecpg-sql-set-descriptor.html" title="SET DESCRIPTOR">SET DESCRIPTOR</a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ecpg-sql-execute-immediate.html" title="EXECUTE IMMEDIATE">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ecpg-sql-commands.html" title="36.14. Embedded SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ecpg-sql-open.html" title="OPEN">Next</a></td></tr><tr><td width="40%" align="left" valign="top">EXECUTE IMMEDIATE </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> OPEN</td></tr></table></div></body></html>