Re: Delete with foreign keys

felix(at)crowfix(dot)com wrote:
> I have three tables --
>
> CREATE TABLE name (id INT PRIMARY KEY, str VARCHAR(20));
> CREATE TABLE place (id INT PRIMARY KEY, name_id INT REFERENCES name(id));
> CREATE TABLE data (id INT PRIMARY KEY, place_id INT REFERENCES place(id));
>
> I want to delete all place and data rows which reference specific
> names, but not the names themselves. I can do it like this:
>
> DELETE FROM data d WHERE exists (SELECT id from place p WHERE d.place_id = p.id AND p.name_id IN (SELECT id FROM name WHERE str LIKE 'Fredonia%'));
>
> DELETE FROM place WHERE name_id IN (SELECT id FROM name WHERE str LIKE 'Fredonia%');
>
> but it seems rather roundabout, and I wonder whether the EXISTS and IN
> business is slow. Is there some way to do it using JOINs? I think of
> something like this:
>
> DELETE FROM place p, name n WHERE p.name_id = n.id AND n.str LIKE 'Fredonia%';
>
> but I don't want to delete the name rows. Then I think of this:
>
> DELETE FROM place p WHERE p.name_id = name.id AND name.str LIKE 'Fredonia%';
>
> but I feel uneasy about the two separate name references when the
> table is not named in the FROM clause. Maybe that's just my novicity.
>
> I also wonder about getting fancy and ending up with SQL specific to a
> database; I don't have any plans to migrate, but I try to avoid
> branding my SQL.
>
>
Hello, I am Dipesh Mistry from Ahmedabad-India.
I have the solution for you.
First drop the constraint on table data.
Example.
alter table data drop constraint data_place_id_fkey;
And in second step add new Constraint.
Example.
alter table data add constraint data_place_id_fkey FOREIGN
KEY(place_id) REFERENCES place(id) ON DELETE CASCADE ON UPDATE CASCADE;

Now when you test query like,

delete from place where name_id in(select id from name where str='dip%');

So, you can try this above step.

--
With Warm Regards,
Dipesh Mistry
Information Technology Dept.
GaneshaSpeaks.com