Re: How to handle a group query

Поиск
Список
Период
Сортировка
От Tom Lane
Тема Re: How to handle a group query
Дата
Msg-id 27973.1099595719@sss.pgh.pa.us
обсуждение исходный текст
Ответ на How to handle a group query  (Nigel Metheringham <Nigel.Metheringham@dev.intechnology.co.uk>)
Ответы Re: How to handle a group query  (Nigel Metheringham <Nigel.Metheringham@dev.intechnology.co.uk>)
Список pgsql-novice
Nigel Metheringham <Nigel.Metheringham@dev.intechnology.co.uk> writes:
> What I am trying to do is get a set of rows out of a table based on a
> set of grouping constraints.  A simplified form of the table I am using
> is:-
>         CREATE TABLE grouptest (
>          rowid serial PRIMARY KEY,
>          grouping integer,
>          tstval integer,
>          other character varying);

> I want to get out rows of data where tstval is at a minimum value for
> each set GROUPed by grouping.   If there is more than one row with the
> same minimal value for tstval then I want any of those rows (but the
> data for a row must be consistent).

If you don't mind using a Postgres-specific construct, SELECT DISTINCT ON
works nicely for this.  See the "weather reports" example in the SELECT
reference page.

            regards, tom lane

В списке pgsql-novice по дате отправления:

Предыдущее
От: Nigel Metheringham
Дата:
Сообщение: How to handle a group query
Следующее
От: "John-Paul Delaney"
Дата:
Сообщение: Re: pg_ [dump & restore] invalid archive problem