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Subject: Re: Delete with join -- deleting related table entries?
Date: Wed, 8 Feb 2006 09:56:28 -0800
Message-ID: <144D12D7DD4EC04F99241498BB4EEDCC20CC6E@nelson.osl.com>
Thread-Topic: [SQL] Delete with join -- deleting related table entries?
Thread-Index: AcYs1v7zEVPPTa00SJuW6NZQPDXtdAAAFnJg
From: "Owen Jacobson" <ojacobson@osl.com>
To: <pgsql-sql@postgresql.org>

Bryce Nesbitt wrote:=20

> Owen Jacobson wrote:
>
> > BEGIN;
> >   DELETE FROM note WHERE issue_id IN (SELECT issue_id FROM isuse
> >     WHERE reservation_id =3D reservation_to_delete);
> >   DELETE FROM isuse WHERE reservation_id =3D reservation_to_delete;
> >   DELETE FROM reservations WHERE reservation_id =3D=20
> reservation_to_delete;
> > COMMIT;
> >
> > With an appropriate value or expression substituted into=20
> > reservation_to_delete.  This would be the "hard way", but (as=20
> > it's in a single transaction) will still protect other=20
> > 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=20
> 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;
>=20
> 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 =3D issue.issue_id
          AND issue.reservation_id =3D reservation.reservation_id
          AND reservation.date > '2006-01-16';
  DELETE FROM issue
    WHERE issue.reservation_id =3D 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 =3D issue.issue_id
          AND issue.reservation_id =3D reservation.reservation_id
          AND reservation.date > '2006-01-16';
  DELETE FROM issue USING reservation
    WHERE issue.reservation_id =3D reservation.reservation_id
          AND reservation.date > '2006-01-16';
  DELETE FROM reservation WHERE date > '2006-01-16';
COMMIT;

The version using subselects works fine, too.

-Owen