Re: short-cutting if sum()>constant

On Tue, 22 Dec 2009 20:47:18 +0100
Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:

> Hello
>
> I found one ugly trick. You can multiply lines and SUM > cons
> could be replaced limit clause:

The trick is really smart (and fun), kudos, really, it's always a
pleasure to read your solutions, thanks.

But as expected:

In a table with 100000 rows with random values [0,9]

test=# select sum(x) from (select 1 as x,(a =
generate_series(1,a))::int from data limit 100000) s;
sum
--------
100000
(1 row)

Time: 71.423 ms

test=# create or replace function tano(a int, out b int)
returns int as
$$
declare
row record;
begin
b :=0;
for row in select a as _a from data
loop
b := row._a + b;
if (b>=a) then
return;
end if;
end loop;
return;
end;
$$ language plpgsql;

test=# select * from tano(100000);
b
--------
100000
(1 row)

Time: 0.187 ms

I run both several times to avoid simple caching issues... anyway I
didn't really run a serious benchmark, but results were always in
the same order of magnitude.

I hope I didn't make any mistake.

--
Ivan Sergio Borgonovo
http://www.webthatworks.it