Re: HELP: aggregating insert rule for multirow inserts.

What about this as a rule. It seems to work for me.

create or replace rule critter_counter as
on INSERT to critter do (

insert into zoostats
select distinct new.legs
where new.legs not in (select legs from zoostats);

update zoostats set headcount = (
select count(*)
from critter
where critter.legs = zoostats.legs
) where zoostats.legs = new.legs
);

===============
OUTPUT (from entire script)
===============
CREATE TABLE
psql:pglist-problem.1.sql:4: NOTICE: CREATE TABLE / PRIMARY KEY will
create implicit index 'zoostats_pkey' for table 'zoostats'
CREATE TABLE
CREATE RULE
INSERT 17347 1
INSERT 17349 1
INSERT 17351 1
INSERT 17353 1
name | legs
----------+------
cat | 4
starfish | 5
ant | 6
dog | 4
(4 rows)

legs | headcount
------+-----------
5 | 1
6 | 1
4 | 2
(3 rows)

INSERT 0 4
legs | headcount
------+-----------
4 | 4
5 | 2
6 | 2
(3 rows)

psql:pglist-problem.1.sql:32: NOTICE: Drop cascades to rule
critter_counter on table critter
DROP TABLE
DROP TABLE
=========
End OUTPUT
=========

(oops forgot to send to list)
--Mike

On 5/4/05, Mischa Sandberg <mischa(dot)sandberg(at)telus(dot)net> wrote:
> I'm having a problem with the use of the NEW rowset,
> in a rule intended to aggregate across inserts.
>
> I've never really grokked how NEW and OLD really work,
> syntactically, other than that they seem to be implicit
> in every top-level FROM clause, and any mention elsewhere
> gets an error: '42P01: relation "*NEW*" does not exist'.
>
> I've tried different flavours of the UPDATE command,
> in the following rule, and they either produce syntax errors
> or the wrong results.
>
> Any suggestions much appreciated ...
>
> ====================== CODE
> "How many critters are in the zoo, of the 4,5,6...-legged varieties?"
>
> create table critter(name text, legs int);
> create table zoostats(legs int, headcount int default 0,
> primary key(legs));
>
> create or replace rule critter_counter as
> on INSERT to critter do (
>
> insert into zoostats
> select distinct new.legs
> where new.legs not in (select legs from zoostats);
>
> update zoostats
> set headcount = headcount + (select count(*)) -- "from new"
> where new.legs = zoostats.legs
> );
>
> insert into critter values('cat',4);
> insert into critter values('starfish',5);
> insert into critter values('ant',6);
> insert into critter values('dog',4);
>
> insert into critter select * from critter; -- double everything.
>
> select * from zoostats;
>
> drop table zoostats cascade;
> drop table critter;
> ====================== EXPECTED OUTPUT
> legs headcount
> ---- ---------
> 4 4
> 5 2
> 6 2
> ====================== ACTUAL OUTPUT
> legs headcount
> ---- ---------
> 4 3 -- !?
> 5 2
> 6 2
> ====================== OTHER ATTEMPT:
> This version of the update looks syntactically right to me,
> but makes CREATE RULE fail on a syntax error:
>
> ...
>
> update zoostats
> set headcount = headcount + tally
> from (select new.legs, count(new.legs) as tally -- from new !?
> group by new.legs) as poll
> where poll.legs = zoostats.legs;
>
> ERROR: 'Subquery in FROM may not refer to other relations
> of same query level'.
> --
> Engineers think equations approximate reality.
> Physicists think reality approximates the equations.
> Mathematicians never make the connection.
>
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