Re: Delete with join -- deleting related table entries?

Bryce Nesbitt wrote:

> Owen Jacobson wrote:
>
> > BEGIN;
> >   DELETE FROM note WHERE issue_id IN (SELECT issue_id FROM isuse
> >     WHERE reservation_id = reservation_to_delete);
> >   DELETE FROM isuse WHERE reservation_id = reservation_to_delete;
> >   DELETE FROM reservations WHERE reservation_id =
> reservation_to_delete;
> > COMMIT;
> >
> > With an appropriate value or expression substituted into
> > reservation_to_delete.  This would be the "hard way", but (as
> > it's in a single transaction) will still protect other
> > clients from seeing a partial delete.
>
> Yup, that's exactly how I delete reservations one a time.   But here I
> need to select a few thousand reservations, and I don't think
> this will
> work:
> BEGIN;
>   DELETE FROM note WHERE issue_id IN (SELECT issue_id FROM isuse
>       WHERE reservation_id IN
>      (select reservation_id from reservations where date > magic);
>   DELETE FROM isuse WHERE reservation_id IN
>      (select reservation_id from reservations where date > magic)
>   DELETE FROM reservations WHERE reservation_id IN
>      (select reservation_id from reservations where date > magic)
> COMMIT;
>
> I suppose I can do the subselect as a perl wrapper, but I was thinking
> that maybe SQL could do it all for me....

Further thinking produced the following functional example.

CREATE TABLE reservation ( reservation_id INTEGER NOT NULL, date DATE NOT NULL
);

CREATE TABLE issue ( issue_id INTEGER NOT NULL, reservation_id INTEGER NOT NULL
);

CREATE TABLE note ( issue_id INTEGER NOT NULL
);

INSERT INTO reservation VALUES (1, '2006-01-01');
INSERT INTO reservation VALUES (2, '2006-01-15');
INSERT INTO reservation VALUES (3, '2006-02-01');

INSERT INTO issue VALUES (1, 1);
INSERT INTO issue VALUES (2, 1);
INSERT INTO issue VALUES (3, 2);
INSERT INTO issue VALUES (4, 2);
INSERT INTO issue VALUES (5, 3);
INSERT INTO issue VALUES (6, 3);

INSERT INTO note VALUES (1);
INSERT INTO note VALUES (2);
INSERT INTO note VALUES (3);
INSERT INTO note VALUES (4);
INSERT INTO note VALUES (5);
INSERT INTO note VALUES (6);

-- PostgreSQL 8.0 and prior
BEGIN; DELETE FROM note   WHERE note.issue_id = issue.issue_id         AND issue.reservation_id =
reservation.reservation_id        AND reservation.date > '2006-01-16'; DELETE FROM issue   WHERE issue.reservation_id =
reservation.reservation_id        AND reservation.date > '2006-01-16'; DELETE FROM reservation WHERE date >
'2006-01-16';
COMMIT;

-- PostgreSQL 8.1 and later
BEGIN; DELETE FROM note USING issue, reservation   WHERE note.issue_id = issue.issue_id         AND
issue.reservation_id= reservation.reservation_id         AND reservation.date > '2006-01-16'; DELETE FROM issue USING
reservation  WHERE issue.reservation_id = reservation.reservation_id         AND reservation.date > '2006-01-16';
DELETEFROM reservation WHERE date > '2006-01-16'; 
COMMIT;

The version using subselects works fine, too.

-Owen