Re: delete on cascade

Στις Δευτέρα 23 Οκτώβριος 2006 11:49, ο/η Luca Ferrari έγραψε:
> Hi all,
> I guess this is an already asked question, but I didn't found an answer, so
> apologize me. Imagine I've got two tables:
> skill(id,description)        // primary key => id
> family(id,description)    // primary key => id
> and I want to associate skills to families:
> ass_sf(id_skill,id_family)    // appropriate foreign keys
>
> Tables are already created and the database is running. Now I'd like to
> implement a delete cascade, thus when I delete a skill also its association
> with the family must be deleted. I gues I should have declared the skill
> table as follows:
> CREATE TABLE skill
> (
>     id varchar(20) on delete cascade,
>     description varchar(50),
>     primary key(id)
> );
>
> right? The problem is: how can I alter the table to add the column

not right!!!
ON DELETE CASCADE is specified in FOREIGN KEY contsraints.
So that would be in ass_sf table.
If you find ALTER TABLE ass_sf command hard to run, then drob your
ass_sf table and define it like

CREATE TABLE ass_sf (
.....
skill_id INT REFERENCES skill(id) ON DELETE CASCADE,
familly_id INT REFERENCES family(id) ON DELETE CASCADE
);

The above causes cascade deletes not only on skills but on families also.

> constraint now, without redeclaring the table?
> Thanks very much for helping me.
> Luca
>
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Achilleas Mantzios