SQL Server：插入，删除后触发

Question

请帮我用SQL语言中的触发器。

我有2个表product_subcategories和Products。

• product_subcategories：id, name, count_products
• Products：id, name, price, id_product_subcategories

必要添加或删除行产品表来更新子类别

例如产品数量时，我们有两个子类别“name = first，count_products = 0”，“name = second，count_products = 0”。当添加到产品表格3行：“name = pr1，price = 1，id_product_subcategories = 1”，“name = np2，price = 2，id_product_subcategories = 1”，“name = PR3，price = 5，id_product_subcategories = 2”

表子类别应该

“NAME =第一，count_products = 2”， “名称=第二，count_products = 1”

这里是我写的，但出于某种原因，他没有一个工作线，而我不明白该怎么做，当你在插入的表中添加几行来遍历每行时？

CREATE TRIGGER 
    countproductscategories 
ON 
    dbo.products 
AFTER 
    INSERT 
AS 
IF @@ROWCOUNT = 1 
BEGIN 
    UPDATE dbo.product_subcategories 
    SET count_products = count_products + 1 
    WHERE dbo.product_subcategories.id = (SELECT id FROM inserted) 
END; 

Answer 1

什么是@@ROWCOUNT = 1？这应该做你想要什么：

CREATE TRIGGER 
    countproductscategories 
ON dbo.products AFTER INSERT 
AS 
BEGIN 
    UPDATE dbo.product_subcategories 
     SET count_products = count_products + 1 
     WHERE dbo.product_subcategories.id IN (SELECT id FROM inserted) 
END; 

如果你想在每次插入只有一行做到这一点，那么你可以做：

CREATE TRIGGER 
    countproductscategories 
ON dbo.products AFTER INSERT 
AS 
BEGIN 
    UPDATE dbo.product_subcategories 
     SET count_products = count_products + 1 
     WHERE dbo.product_subcategories.id IN (SELECT id FROM inserted) AND 
       (SELECT COUNT(*) FROM inserted) = 1; 
END;