如何使用触发器来增加或减少mysql中的库存

Question

我正在创建一个 MySQL 数据库。我有两个不同的表：用于销售（

id, idoftheproduct, quantity

）和用于供应（

id, idoftheproduct, quantity

）。我想要一个触发器，每当我们添加新的销售或新的供应时，它都会增加或减少称为 Stock(

idoftheproduct, quantity

)

的不同表的值

Answer 1

简而言之，不要。相反，创建一个视图：

CREATE VIEW Stock
AS
    SELECT  IDofTheProduct, SUM(Quantity) AS Quantity
    FROM    (   SELECT  IDofTheProduct, Quantity
                FROM    Supplies
                UNION ALL
                SELECT  IdOfTheProduct, -Quantity
                FROM    Sales
            ) t
    GROUP BY IDofTheProduct;

这样，无论您的基础表发生变化，您的视图都会发生变化。这在更新/插入期间的开销较小，并且始终准确，即使触发器由于某种原因没有触发。

编辑

抱歉，我忘记了 MySQL 不允许在视图中使用子查询。一种解决方案是创建一个新视图来代替子查询：

CREATE VIEW SalesAndSupplies
AS
    SELECT  'Supplies' AS `Type`,
            IDofTheProduct, 
            Quantity
    FROM    Supplies
    UNION ALL
    SELECT  'Sales' AS `Type`,
            IDofTheProduct, 
            -Quantity
    FROM    Sales;

CREATE VIEW Stock
AS
    SELECT  IDofTheProduct, SUM(Quantity) AS Quantity
    FROM    SalesAndSupplies
    GROUP BY IDofTheProduct;

SQL Fiddle 示例

Answer 2

带有视图的解决方案是一个很好的解决方案，但随着时间的推移，它往往会变得更慢，特别是如果您有大量销售和供应数据，因为您总是计算它。

因此，如果您决定通过触发器来实现它，那么您必须至少有四个触发器（在两个表上插入和删除）。由于它们都更新了库存，因此最好将部分代码分解为存储过程。

更新库存的存储过程

CREATE PROCEDURE sp_update_stock(IN pid INT, IN qty DECIMAL(11, 3))
    INSERT INTO stock (idoftheproduct, quantity) 
    VALUES (pid, qty)
    ON DUPLICATE KEY UPDATE quantity = quantity + qty;

如果执行时不存在带有

idoftheproduct

的行，则会创建该行。否则，它将更新以反映更改。

现在触发

CREATE TRIGGER tg_sales_insert
AFTER INSERT ON sales
FOR EACH ROW
    CALL sp_update_stock(NEW.idoftheproduct, -1 * NEW.quantity);

 CREATE TRIGGER tg_supplies_insert
 AFTER INSERT ON supplies
 FOR EACH ROW
    CALL sp_update_stock(NEW.idoftheproduct, NEW.quantity);

CREATE TRIGGER tg_sales_delete
AFTER DELETE ON sales
FOR EACH ROW
    CALL sp_update_stock(OLD.idoftheproduct, OLD.quantity);

CREATE TRIGGER tg_supplies_delete
AFTER DELETE ON supplies
FOR EACH ROW
    CALL sp_update_stock(OLD.idoftheproduct, -1 * OLD.quantity);

现在您可以在销售和供应中插入和删除。

INSERT INTO Supplies VALUES (NULL, 1, 100), (NULL, 1, 50), (NULL, 1, 75);
INSERT INTO Sales VALUES (NULL, 1, 2),(NULL, 1, 10), (NULL, 1, 5);
DELETE FROM Sales WHERE id = 1;
DELETE FROM Supplies WHERE id = 3;

如果看一下

stock

就会看到

|产品的IDO数量 |
----------------------------
| 1 | 135 | 135

这里是SQLFiddle演示

Answer 3

我和你有同样的情况，如果我要创建一个供应商，销售，detail_stock和detail_supplier表，那么前面有名称detail的表将包含主键列，外键来自商品和供应商表，供应商发货金额（针对供应商发货明细），采购金额（针对采购表），最后是采购状态或供应商发货状态（这里我每个明细都使用两种状态）。我使用此状态来触发我作为下面的查询创建的触发器。

-- TRIGGER
DELIMITER /
CREATE TRIGGER trigger_update_purchase
AFTER INSERT ON detail_status_transaction
FOR EACH ROW
BEGIN
    DECLARE quantity_of_items_purchased  INT;

    SET quantity_of_items_purchased = NEW.quantity_purchased;

    IF NEW.status_transaction = 'Completed' THEN
        -- Update stock_book
        UPDATE book
        SET stock_book = stock_book - quantity_of_items_purchased 
        WHERE book_id = (SELECT book_id FROM transaction WHERE id_nota = NEW.transaction_id);
    elseif NEW.transaction_status = 'Refund' then
        update book
        set stock_book = stock_book + quantity_of_items_purchased 
        where id_book = (select book_id from transaction where id_nota = NEW.transaction_id);
    END IF;
END;
DELIMITER ;

触发更新供应商

DELIMITER /
CREATE TRIGGER trigger_update_supplier
AFTER INSERT ON detail_status_supplier
FOR EACH ROW
BEGIN
    DECLARE  quantity_buy_items INT;

    SET  quantity_buy_items= NEW.quantity_shipped;

    IF NEW.status_supplier = 'Success' THEN
        -- Update book stock (supplier)
        UPDATE book
        SET stock_book = stock_book + quantity_buy_items
        WHERE id_book = (SELECT id_book FROM book WHERE id_book = NEW.book_id);
    elseif NEW.status_supplier = 'Failed' then
        update book
        set stock_book = stock_book -  quantity_buy_items
        where id_book = (SELECT id_book FROM book WHERE id_book = NEW.book_id);
    END IF;
END;
DELIMITER ;

然后通过在details表中输入输入来触发此触发器，将使库存根据触发的内容和所需的条件减少或增加。