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 method returns 0 for zero results and false for an unsupported statement, it is recommended to use === if testing for zero or false.

/*
 * 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 false
 */