Re: short-cutting if sum()>constant

Hello

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

postgres=# select * from data;
a
---
3
2
1
4
2
3
(6 rows)

Then SELECT * FROM WHERE and stop when SUM(a) = n

then

postgres=# select generate_series(1,a) from data;
generate_series
-----------------
1
2
3
1
2
1
1
2
3
4
1
2
1
2
3

So If I would to check if there are sum(a) >= 10 then I can use LIMIT
10. If query returns ten rows, then result is true, else result is
false

select a, (a = generate_series(1,a))::int from data limit 12; -- stop
after sum(a) = 12

postgres=# select sum(x) from (select 1 as x,(a =
generate_series(1,a))::int from data limit 12) s;
sum
-----
12 -- 12 is eq 12, so test is successful

(1 row)

Regards
Pavel Stehule

2009/12/22 Ivan Sergio Borgonovo <mail(at)webthatworks(dot)it>:
> Hi,
>
> I'd like to know if
>
> select sum(qty) from t where status=37;
>
> is > constant.
>
> qty is always >0.
>
> Is there a way to skip examining further rows and return a result
> ASAP?
>
>
> --
> Ivan Sergio Borgonovo
> http://www.webthatworks.it
>
>
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