CREATE TABLE part (id, pid);
INSERT INTO part VALUES ( 1 , 0 );
INSERT INTO part VALUES ( 1 , 1 );
INSERT INTO part VALUES ( 2 , 1 );
INSERT INTO part VALUES ( 3 , 1 );
INSERT INTO part VALUES ( 4 , 1 );

CREATE TRIGGER part_delete AFTER DELETE ON part
BEGIN
	DELETE FROM part WHERE pid = old.id AND pid !=  0 ;
	INSERT INTO test_trigger VALUES(old.id); -- тестирование
END;
CREATE TABLE test_trigger(id); -- таблица для проверки

DELETE FROM part WHERE id =  1  AND pid =  0 ;