In article <461D0B1A.6030407@xxxxxxxxxxxxxxxx>,
Chris Travers <chris@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
% DO ALSO rules involving NEW are fundamentally dangerous to the integrity
% of data because NEW is not guaranteed to be internally consistent. DO
% INSTEAD rules are fine (there is only one NEW), as are any DO ALSO rules
% involving OLD.
It seems to me that this sort of dogmatism is fundamentally dangerous.
CREATE TABLE x (a varchar(20) PRIMARY KEY, b INT NOT NULL);
CREATE TABLE y (a varchar(20) NOT NULL, b INT NOT NULL);
CREATE RULE y_ins AS ON INSERT TO y DO UPDATE x SET b=b+new.b WHERE a=new.a;
CREATE RULE y_del AS ON DELETE TO y DO UPDATE x SET b=b-old.b WHERE a=old.a;
INSERT INTO x VALUES ('a', 0);
INSERT INTO y VALUES ('a', 2);
INSERT INTO y VALUES ('a', 2);
SELECT * FROM x;
a | b
---+---
a | 4
DELETE FROM y;
SELECT * FROM x;
a | b
---+---
a | 2
The DO ALSO rules involving OLD didn't do so well here.
The section on rules v. triggers could do with a caveat or two, but
it's a bit much to call them "fundamentally dangerous".
--
Patrick TJ McPhee
North York Canada
ptjm@xxxxxxxxxxxx
