如何创建外键所以当我们删除子级中的父值时将更新为null

Question

我是T-SQL的新手,请帮忙:我有两张桌子

User
  Id
  Name

History
  Id
  Result
  UserId

如何创建关系,一旦我从User表中删除User,则会将UserId列的History表更新为NULL

Answer 1

你可以on delete set null像这样使用

ALTER TABLE USERS 
ADD CONSTRAINT Users_ThemeID_FK 
FOREIGN KEY (ThemeID) REFERENCES Themes(ThemeID) 
ON DELETE SET NULL