Re: help on select

On 2011-04-20, Saulo Venâncio <saulo(dot)venancio(at)gmail(dot)com> wrote:
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> Hi guys,
> I need your help.
> I have a table called medidas, in this table i have some ocurrences that ha=
> s
> id_medida(primary key) id_ponto (sec_key) and also datetime field as
> timestamp.
> i would like to know from a set of idpontos, e.g. 10,11,23,24.... how can i
> get the most recent date that is common to all??
> for example, if idponto das date 2011-02-03 but none of others have this
> date in the db i dont want this. i want one common for all..
> thanks.

the trick seems to be to GROUP BY datetime
and to use a HAVING clause to reject the unwanted groups using
count(distinct()) to ensure coverage of the list.

-- a table

create temp table medidas(id_medida serial,id_ponto integer,datetime timestamp);

-- some test data.

insert into medidas (id_ponto,datetime) select floor(random()*30+1),('today'::timestamp +
floor(generate_series(0,100000)/10)*'1s'::interval);

-- the query:
-- note you need to paste the list of number in two different places
-- in the query, postgres only counts the length once.

select datetime
from medidas
where id_ponto in (10,11,23,24,27)
group by datetime
having count(distinct(id_ponto)) = array_length( array[10,11,23,24,27],1)
order by datetime desc limit 1;

-- confirmation

select * from medidas where datetime = (
select datetime
from medidas
where id_ponto in (10,11,23,24,27)
group by datetime
having count(distinct(id_ponto)) = array_length(array[10,11,23,24,27],1)
order by datetime desc limit 1
)
order by id_ponto;

what's this for?
Are you looking at keno results to see how recently your pick would have won?

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