Question

我有两个名为sale和customer的表。我想创建一个触发器，用于更新last_purchase表中每个新插入的customer表上的列sale。

表客户：customer_id，name，last_sale，...
表销售：sale_id，customer_id，date，...

CREATE TRIGGER update_last_sale BEFORE INSERT ON sale FOR EACH ROW EXECUTE...

我已经开始写作，但我不知道该怎么做有人能帮助我吗？

Answer 1

CREATE FUNCTION update_customer_last_sale() RETURNS TRIGGER AS $$
BEGIN
    UPDATE customer SET last_sale=now() WHERE cutomer_id=NEW.customer_id;
    RETURN NEW;
END; $$
LANGUAGE plpgsql;

然后

CREATE TRIGGER update_last_sale
BEFORE INSERT ON sale
FOR EACH ROW EXECUTE update_customer_last_sale;

NEW是即将插入销售表中的行。（对于更新行，更新后行的显示方式为NEW，更新前行的显示方式为OLD。

Answer 2

基本上，我认为存储冗余数据不是一个好主意。客户中的last_sale列只是max（sales.sale_date）的汇总。

如果我们使用now（）来触摸customers.last_date，情况会更糟。如果我们需要重新插入一些历史记录（例如重新计算去年的税收）会发生什么。这就是存储冗余数据时的结果....

-- modelled after Erwin's version
SET search_path='tmp';

-- DROP TABLE customers CASCADE;
CREATE TABLE customers
    ( id INTEGER NOT NULL PRIMARY KEY
    , name VARCHAR
    , last_sale DATE
    );

-- DROP TABLE sales CASCADE;
CREATE TABLE sales
    ( id INTEGER NOT NULL PRIMARY KEY
    , customer_id INTEGER REFERENCES customers(id)
    , saledate DATE NOT NULL
    );


CREATE OR REPLACE FUNCTION update_customer_last_sale() RETURNS TRIGGER AS $meat$
BEGIN
    UPDATE customers cu
    -- SET last_sale = now() WHERE id=NEW.customer_id
    SET last_sale = (
        SELECT MAX(saledate) FROM sales sa
        WHERE sa.customer_id=cu.id
        )   
    WHERE cu.id=NEW.customer_id
    ;
    RETURN NEW;
END; $meat$
LANGUAGE plpgsql;

CREATE TRIGGER update_last_sale
    AFTER INSERT ON sales
    FOR EACH ROW
    EXECUTE PROCEDURE update_customer_last_sale();


INSERT INTO customers(id,name,last_sale) VALUES(1, 'Dick', NULL),(2, 'Sue', NULL),(3, 'Bill', NULL);


INSERT INTO sales(id,customer_id,saledate) VALUES (1,1,'1900-01-01'),(2,1,'1950-01-01'),(3,2,'2011-12-15');

SELECT * FROM customers;

SELECT * FROM sales;

结果：

 id | name | last_sale  
----+------+------------
  3 | Bill | 
  1 | Dick | 1950-01-01
  2 | Sue  | 2011-12-15
(3 rows)

 id | customer_id |  saledate  
----+-------------+------------
  1 |           1 | 1900-01-01
  2 |           1 | 1950-01-01
  3 |           2 | 2011-12-15
(3 rows)

Answer 3

我想你想要这条规则。

CREATE RULE therule AS ON INSERT TO sale DO ALSO
    (UPDATE customer SET customer.last_sale = now()
           WHERE customer.customer_id=NEW.customer_id);

编辑：但请参阅评论中的讨论。

触发更新Postgres 9中的当前日期

3 个答案: