To: pgsql-sql@postgresql.org
From: Jasen Betts <jasen@xnet.co.nz>
Subject: Re: help on select
Date: 21 Apr 2011 23:15:26 GMT
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On 2011-04-20, Saulo Venâncio <saulo.venancio@gmail.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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