SQL 级联删除查询
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Cascade Delete Query
提问by Nits
I have three tables. Product, Company, Employee
我有三张桌子。产品、公司、员工
ProductId of Product table is foregin key for Company and CompanyId of Company table is foregin key for Employee
Product 表的 ProductId 是 Company 的外键，Company 表的 CompanyId 是 Employee 的外键
So on deleting ProductId from Product table, all the related records in other tables should delete. But I can't touch schema(can't use alter table). How should I write the query in that case..
因此，在从 Product 表中删除 ProductId 时，其他表中的所有相关记录都应删除。但我无法触摸架构（不能使用更改表）。在这种情况下我应该如何编写查询..
回答by Erich Kitzmueller
If you can't add constraints that propagates the delete, you have to write all the necessary deletes yourself:
如果您无法添加传播删除的约束，则必须自己编写所有必要的删除：
delete employee where companyid in (select companyid from company c where productid = xxx);
delete company where productid=xxx;
delete product where productid=xxx;
回答by Pravin Satav
Try this option. I don't have environment to test this. I guess with some changes it should work at your end.
试试这个选项。我没有环境来测试这个。我想通过一些更改，它应该可以在您的最后工作。
DELETE Product,Company,Employee
FROM
user LEFT JOIN items ON product.productid = company.productid
LEFT JOIN orders ON company.productid = product.productid
WHERE product.productid = [$productid]
