Bruce Momjian <pgman@candle.pha.pa.us> wrote:
> Magnus Naeslund(f) wrote:
>>> select id, sum(sum_col)||'/'||count(*) from table_name
>>> group by id;
>>>
>>> or
>>>
>>> select table_name.id, sum(sum_col)||'/'||t2.count from table_name,
>>> (select id, count(*) as count from table_name group by id) as t2
>>> where table_name.id=t2.id group by table_name.id,t2.count;
>>>
>>
>> Give it up already, i was MAKING A POINT, not trying to make an
>> optimized count(*) thing :)
>> There are other examples that you cannot get around, that will be
>> evaluated more than once when a local "user variable" would make it
>> not need to.
>
> Here's an even slimmer query that makes a var:
>
> test=> select var1.* from (select 1) as var1;
> ?column?
> ----------
> 1
> (1 row)
Good!
Now convert this query so that it only evaluates the date_part thing
ONCE:
select t.id, date_part('days',now()-t.stamp) from table_name t where
date_part('days',now()-t.stamp) > 20;
I hope you all are kidding me in not seeing the real issue i'm trying to
show here.
Cheers
Magnus
