如何基于其他表中的数据在表上创建SQLite触发器？

Question

我有两个表-

part(partID, brand, price, size)

consists_of(customerID, partID, quantity, price, shipdate)
                        |
                        FK part.ID from part

表part永远不会被更改/更新，但是consists_of将会被更改。

1. 如何在consists_of上添加[插入之前？]触发器，以检查每个条目的consists_of.price是否小于或等于特定consists_of.quantity * part.price的consists_of.partID并引发异常终止？

或，

2. 如何在consists_of上添加[插入后？]触发器，该触发器是否使INSERT INTO consists_of(price) VALUES (...)的值等于consists_of.price的consists_of.quantity * part.price的consists_of.partID？

Answer 1

如果我对您的理解正确，则可以在子查询中选择part.price并计算part.price * consists_of.quantitiy。

1. 插入前

CREATE TABLE part(part_id INTEGER, price INTEGER);
CREATE TABLE consists_of(customer_id INTEGER, part_id INTEGER, quantity INTEGER, price INTEGER);

INSERT INTO part VALUES(10, 50);
INSERT INTO part VALUES (20, 1000);

CREATE TRIGGER IF NOT EXISTS raise_if_consists_of_price_too_expensive
AFTER INSERT ON consists_of
WHEN new.price > (SELECT part.price * new.quantity FROM part WHERE part.part_id = new.part_id)
BEGIN
  SELECT RAISE (ABORT, 'too expensive.');
END;

 -- OK
INSERT INTO consists_of(customer_id, part_id, quantity, price)
VALUES(10050, 20, 31, 100);
 -- OK
INSERT INTO consists_of(customer_id, part_id, quantity, price)
VALUES(80030, 10, 9, 50 * 9);
 -- Raise abort
INSERT INTO consists_of(customer_id, part_id, quantity, price)
VALUES(80099, 10, 9, 50 * 9 + 1);

2. 插入后

CREATE TABLE part(part_id INTEGER, price INTEGER);
CREATE TABLE consists_of(customer_id INTEGER, part_id INTEGER, quantity INTEGER, price INTEGER);

INSERT INTO part VALUES(10, 50);
INSERT INTO part VALUES (20, 1000);

CREATE TRIGGER IF NOT EXISTS fill_consists_of_price
AFTER INSERT ON consists_of
BEGIN
  UPDATE consists_of
  SET
  price = (
    SELECT consists_of.quantity * part.price
    FROM part
    WHERE part.part_id = consists_of.part_id
  )
  WHERE customer_id = new.customer_id AND part_id = new.part_id
  ;
END;

INSERT INTO consists_of(customer_id, part_id ,quantity)
VALUES(10050, 20, 31);

INSERT INTO consists_of(customer_id, part_id ,quantity)
VALUES(80033, 10, 9);