The following bug has been logged online:

Bug reference: 1676
Logged by: Olleg Samoylov
Email address: olleg@mipt.ru
PostgreSQL version: 7.4.7
Operating system: on x86_64-pc-linux-gnu, compiled by GCC x86_64-linux-gcc
(GCC) 3.3.5 (Debian 1:3.3.5-12)
Description: Statment order in rules
Details:

-- Here example for delete rule, but for update rule bug arised also.
-- This is simplified example from working database.
-- create tables
-- counter
create table c (c integer);
insert into c values (0);
-- private table
create table a (a integer);
-- public view
create view v as select a from a;

-- create worked rules, for example
create rule insert_last as on insert to v do instead (update c set
c=c+1;insert into a values (new.a));
create rule delete_last as on delete to v do instead (update c set
c=c-1;delete from a where a=old.a);

insert into v values (0);
select * from a;
-- 1 row
select * from c;
-- 1

delete from v where a=0;
select * from a;
-- 0 rows
select * from c;
-- 0, Okey

-- now change order of statment
drop rule insert_last on v;
drop rule delete_last on v;
create rule insert_first as on insert to v do instead (insert into a values
(new.a);update c set c=c+1);
create rule delete_first as on delete to v do instead (delete from a where
a=old.a;update c set c=c-1);

insert into v values (0);
select * from a;
-- 1 row
select * from c;
-- 1, Ok

delete from v where a=0;
select * from a;
-- 0 row, as expected :-)
select * from c;
-- 1, this is incorrect

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"Olleg Samoylov" <olleg@mipt.ru> writes:
> create rule delete_first as on delete to v do instead (delete from a where
> a=old.a;update c set c=c-1);

> delete from v where a=0;
> select * from a;
> -- 0 row, as expected :-)
> select * from c;
> -- 1, this is incorrect

This isn't a bug. The DELETE causes the a=0 row to disappear from the
view, so the subsequent statement (which is implicitly conditional on
there being an a=0 row) doesn't do anything. If it did do something,
then a "delete from v" that didn't delete any rows would still decrement
c, which is not what you want, eh?

regards, tom lane

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