(PHP 4 >= 4.2.0, PHP 5, PHP 7)
pg_cancel_query — ȡ���첽��ѯ
$connection
pg_cancel_query() ȡ���� pg_send_query() ���͵��첽��ѯ������ȡ���� pg_query() ִ�еIJ�ѯ��
�μ� pg_send_query() �� pg_connection_busy()��