Обсуждение: Opposite value for RESTRICT in foreign keys?

I apologize if this is a simple question, but after much searching
through google and the list archives, I cannot find any answer.  My
question is this:

Say I have two tables:

CREATE TABLE products(
id int,
name varchar(50)
);

CREATE TABLE orders(
id int,
product_id int,
customer varchar(100)
FOREIGN KEY (product_id) REFERENCES products(id) ON UPDATE CASCADE ON
DELETE ???
);


Is there any way to create a foreign key that *allows* you to delete the
matching row from the referenced table (i.e. does the opposite of "NO
ACTION" or "RESTRICT")?

Basically, what I want to happen is:

* Whenever an order is created, the product_id field in the new record
MUST match an existing id field in the products table. (I don't want to
take orders for products that don't exist.)
* Whenver a product id is changed, all corresponding product_id's in the
orders table MUST be updated.  (I want orders to match their respective
products even when the product's id is changed.)
* Whenever a product is deleted, all corresponding product_id's MUST NOT
be changed or deleted.  (Even though the product is gone, I still want
the product_id to stay the same.)

As you can see I need referential integrity for every operation EXCEPT
deletion.

Is there any solution for this without scrapping the foreign key
altogether?

Thanks,

Brian Sanders
Webmaster
The Hotchkiss School
bsanders@hotchkiss.org
860-435-3141

Brian Sanders wrote:
> I apologize if this is a simple question, but after much searching
> through google and the list archives, I cannot find any answer.  My
> question is this:
>
> Say I have two tables:
>
> CREATE TABLE products(
> id int,
> name varchar(50)
> );
>
> CREATE TABLE orders(
> id int,
> product_id int,
> customer varchar(100)
> FOREIGN KEY (product_id) REFERENCES products(id) ON UPDATE CASCADE ON
> DELETE ???
> );
>
>
> Is there any way to create a foreign key that *allows* you to delete the
> matching row from the referenced table (i.e. does the opposite of "NO
> ACTION" or "RESTRICT")?
>
> Basically, what I want to happen is:
>
> * Whenever an order is created, the product_id field in the new record
> MUST match an existing id field in the products table. (I don't want to
> take orders for products that don't exist.)
> * Whenver a product id is changed, all corresponding product_id's in the
> orders table MUST be updated.  (I want orders to match their respective
> products even when the product's id is changed.)
> * Whenever a product is deleted, all corresponding product_id's MUST NOT
> be changed or deleted.  (Even though the product is gone, I still want
> the product_id to stay the same.)
>
> As you can see I need referential integrity for every operation EXCEPT
> deletion.
>
> Is there any solution for this without scrapping the foreign key
> altogether?

Not with referential integrity as per specification. It has to guarantee
the integrity at all times, not just at reference creation. You have to
do this with custom triggers.


Jan

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