The function affected_rows() returns the number of rows affected (add/change/delete) by the last SQL statement executed, or false if the database does not support the function or the statement is not an update. See the driver documentation for support. Most multi-user databases support the command

Because the connection only supports a single global instance of this variable, it is important to retrieve the value of this method before executing another SQL statement (of any type).

/*
 * connection assumed
 */
$db->execute('DELETE FROM act WHERE actno = 20');
 
print $db->affected_rows();
/*
 * Returns 1
 */
 
$db->execute('SELECT FROM act');
print $db->affected_rows();
/*
 * Returns null
 */