connections:
<programlisting><![CDATA[
#include <stdio.h>

EXEC SQL BEGIN DECLARE SECTION;
    char dbname[1024];
EXEC SQL END DECLARE SECTION;

int
main()
{
    EXEC SQL CONNECT TO testdb1 AS con1 USER testuser;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;
    EXEC SQL CONNECT TO testdb2 AS con2 USER testuser;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;
    EXEC SQL CONNECT TO testdb3 AS con3 USER testuser;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;

    /* This query would be executed in the last opened database "testdb3". */
    EXEC SQL SELECT current_database() INTO :dbname;
    printf("current=%s (should be testdb3)\n", dbname);

    /* Using "AT" to run a query in "testdb2" */
    EXEC SQL AT con2 SELECT current_database() INTO :dbname;
    printf("current=%s (should be testdb2)\n", dbname);

    /* Switch the current connection to "testdb1". */
    EXEC SQL SET CONNECTION con1;

    EXEC SQL SELECT current_database() INTO :dbname;
    printf("current=%s (should be testdb1)\n", dbname);

    EXEC SQL DISCONNECT ALL;
    return 0;
}
]]></programlisting>

   This example would produce this output:
<screen>
current=testdb3 (should be testdb3)
current=testdb2 (should be testdb2)
current=testdb1 (should be testdb1)
</screen>
  </para>

  <para>
  The third option is to declare an SQL identifier linked to
  the connection, for example:
<programlisting>
EXEC SQL AT <replaceable>connection-name</replaceable> DECLARE <replaceable>statement-name</replaceable> STATEMENT;
EXEC SQL PREPARE <replaceable>statement-name</replaceable> FROM :<replaceable>dyn-string</replaceable>;
</programlisting>
   Once you link an SQL identifier to a connection, you execute dynamic SQL
   without an AT clause. Note that this option behaves like preprocessor
   directives, therefore the link is enabled only in the file.
  </para>
  <para>
   Here is an example program using this option:
<programlisting><![CDATA[
#include <stdio.h>

EXEC SQL BEGIN DECLARE SECTION;
char dbname[128];
char *dyn_sql = "SELECT current_database()";
EXEC SQL END DECLARE SECTION;

int main(){
  EXEC SQL CONNECT TO postgres AS con1;
  EXEC SQL CONNECT TO testdb AS con2;
  EXEC SQL AT con1 DECLARE stmt STATEMENT;
  EXEC SQL PREPARE stmt FROM :dyn_sql;
  EXEC SQL EXECUTE stmt INTO :dbname;
  printf("%s\n", dbname);

  EXEC SQL DISCONNECT ALL;
  return 0;
}
]]></programlisting>

   This example would produce this output, even if the default connection is testdb:
<screen>
postgres
</screen>
  </para>
  </sect2>

  <sect2 id="ecpg-disconnect">
   <title>Closing a Connection</title>

  <para>
   To close a connection, use the following statement:
<programlisting>
EXEC SQL DISCONNECT <optional><replaceable>connection</replaceable></optional>;
</programlisting>
   The <replaceable>connection</replaceable> can be specified
   in the following ways:

   <itemizedlist>
    <listitem>
     <simpara>
      <literal><replaceable>connection-name</replaceable></literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal>CURRENT</literal>
     </simpara>
    </listitem>

    <listitem>
     <simpara>
      <literal>ALL</literal>
     </simpara>
    </listitem>
   </itemizedlist>

   If no connection name is specified, the current connection is
   closed.
  </para>

  <para>
   It is good style that an application always explicitly disconnect
   from every connection it opened.
  </para>
  </sect2>

 </sect1>

 <sect1 id="ecpg-commands">
  <title>Running SQL Commands</title>

  <para>
   Any SQL command can be run from within an embedded SQL application.
   Below are some examples of how to do that.
  </para>

  <sect2 id="ecpg-executing">
   <title>Executing SQL Statements</title>

  <para>
   Creating a table:
<programlisting>
EXEC SQL CREATE TABLE foo (number integer, ascii char(16));
EXEC SQL CREATE UNIQUE INDEX num1 ON foo(number);
EXEC SQL