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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>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><div xmlns="http://www.w3.org/TR/xhtml1/transitional" 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 11.5 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></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">
GET 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> [, ... ]
GET 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> [, ... ]
</pre></div><div class="refsect1" id="id-1.7.5.20.10.3"><h2>Description</h2><p>
<code class="command">GET DESCRIPTOR</code> retrieves information about a
query result set from an SQL descriptor area and stores it into
host variables. A descriptor area is typically populated
using <code class="command">FETCH</code> or <code class="command">SELECT</code>
before using this command to transfer the information into host
language variables.
</p><p>
This command has two forms: The first form retrieves
descriptor <span class="quote">“<span class="quote">header</span>”</span> items, which apply to the result
set in its entirety. One example is the row count. The second
form, which requires the column number as additional parameter,
retrieves information about a particular column. Examples are
the column name and the actual column value.
</p></div><div class="refsect1" id="id-1.7.5.20.10.4"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>descriptor_name</code></em></span></dt><dd><p>
A descriptor name.
</p></dd><dt><span class="term"><em class="replaceable"><code>descriptor_header_item</code></em></span></dt><dd><p>
A token identifying which header information item to retrieve.
Only <code class="literal">COUNT</code>, to get the number of columns in the
result set, is currently supported.
</p></dd><dt><span class="term"><em class="replaceable"><code>column_number</code></em></span></dt><dd><p>
The number of the column about which information is to be
retrieved. The count starts at 1.
</p></dd><dt><span class="term"><em class="replaceable"><code>descriptor_item</code></em></span></dt><dd><p>
A token identifying which item of information about a column
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> for
a list of supported items.
</p></dd><dt><span class="term"><em class="replaceable"><code>cvariable</code></em></span></dt><dd><p>
A host variable that will receive the data retrieved from the
descriptor area.
</p></dd></dl></div></div><div class="refsect1" id="id-1.7.5.20.10.5"><h2>Examples</h2><p>
An example to retrieve the number of columns in a result set:
</p><pre class="programlisting">
EXEC SQL GET DESCRIPTOR d :d_count = COUNT;
</pre><p>
</p><p>
An example to retrieve a data length in the first column:
</p><pre class="programlisting">
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;
</pre><p>
</p><p>
An example to retrieve the data body of the second column as a
string:
</p><pre class="programlisting">
EXEC SQL GET DESCRIPTOR d VALUE 2 :d_data = DATA;
</pre><p>
</p><p>
Here is an example for a whole procedure of
executing <code class="literal">SELECT current_database();</code> and showing the number of
columns, the column data length, and the column data:
</p><pre class="programlisting">
int
main(void)
{
EXEC SQL BEGIN DECLARE SECTION;
int d_count;
char d_data[1024];
int d_returned_octet_length;
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 ALLOCATE DESCRIPTOR d;
/* Declare, open a cursor, and assign a descriptor to the cursor */
EXEC SQL DECLARE cur CURSOR FOR SELECT current_database();
EXEC SQL OPEN cur;
EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d;
/* Get a number of total columns */
EXEC SQL GET DESCRIPTOR d :d_count = COUNT;
printf("d_count = %d\n", d_count);
/* Get length of a returned column */
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;
printf("d_returned_octet_length = %d\n", d_returned_octet_length);
/* Fetch the returned column as a string */
EXEC SQL GET DESCRIPTOR d VALUE 1 :d_data = DATA;
printf("d_data = %s\n", d_data);
/* Closing */
EXEC SQL CLOSE cur;
EXEC SQL COMMIT;
EXEC SQL DEALLOCATE DESCRIPTOR d;
EXEC SQL DISCONNECT ALL;
return 0;
}
</pre><p>
When the example is executed, the result will look like this:
</p><pre class="screen">
d_count = 1
d_returned_octet_length = 6
d_data = testdb
</pre><p>
</p></div><div class="refsect1" id="id-1.7.5.20.10.6"><h2>Compatibility</h2><p>
<code class="command">GET DESCRIPTOR</code> is specified in the SQL standard.
</p></div><div class="refsect1" id="id-1.7.5.20.10.7"><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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ecpg-sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ecpg-sql-open.html">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">Home</a></td><td width="40%" align="right" valign="top"> OPEN</td></tr></table></div></body></html>
