TSQL 更改表为删除和更新的级联添加约束 [英] TSQL alter table adding constraint for both cascade on delete and update

问题描述

我正在尝试在 tsql 中创建对更新和删除的约束.我尝试了几种不同的方法，现在我有点卡住了&沮丧 - 似乎很简单.我知道您无法更改现有约束，因此我不确定如何执行此操作；

I'm trying to create a constraint with both on update and delete in tsql. I've tried a couple of different methods, and now I'm a little stuck & frustrated - seems so simple. I know you can't alter an existing constraint so I'm not sure about how to do this;

alter table AllowedCars 
   add constraint FK_AllowedCars_CarID foreign key (CarID) 
      references Cars(LocusID) on delete cascade, 
constraint FK_AllowedCars_CarID foreign key (CarID) 
   references Cars(CarID) on update cascade

或者这个；

alter table AllowedCars add constraint FK_AllowedCars_CarID foreign key (CarID) 
   references Cars(CarID) on delete cascade and on update cascade

推荐答案

您需要先删除约束，然后重新创建它.您的第二次尝试是正确的，但您需要删除 和.

You need to drop constraint first, and then recreate it. Your second attempt was right, but you needed to remove and.

alter table AllowedCars 
  drop constraint FK_AllowedCars_CarID 

alter table AllowedCars 
  add constraint FK_AllowedCars_CarID 
      foreign key (CarID) 
      references Cars(CarID) 
      on delete cascade 
      on update cascade

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