Re: Merging timeseries in postgres - Mailing list pgsql-general

From Nick Babadzhanian
Subject Re: Merging timeseries in postgres
Date
Msg-id 663129846.34292.1468498708144.JavaMail.zimbra@cobra.ru
Whole thread Raw
In response to Merging timeseries in postgres  (Tim Smith <randomdev4+postgres@gmail.com>)
Responses Re: Merging timeseries in postgres
List pgsql-general
Whats exactly is wrong with the following query?

select
        dx date,
        nx,
        nx1
    from
        test t
            join test1 t1 on t.dx=t1.dx1
;



----- Original Message -----
From: "Tim Smith" <randomdev4+postgres@gmail.com>
To: "pgsql-general" <pgsql-general@postgresql.org>
Sent: Thursday, July 14, 2016 2:56:19 PM
Subject: [GENERAL] Merging timeseries in postgres

Hi,

I've got a bit of query-writers block ! I've tried various join styles
but can't get it to do what I want to achieve.

Assume I have a bunch of time-series tables :

create table test(dx date,n numeric);
create table test1(dx1 date,nx1 numeric);
insert into test values('2000-01-01','0.001');
insert into test1 values('2002-01-02','0.002');
insert into test1 values('2003-01-03','0.002');

What I want to do is create a view that merges these together with
time as the index, i.e the output would look like :


2000-01-01  0.001  (null)
2002-01-02  (null)   0.002
2003-01-03  (null)   0.003

I can't quite figure out how to keep the index independent and make a
clean join, typical outer join constructs end up with results like :

 dx | nx |    dx1     |  nx1
----+----+------------+-------
    |    | 2002-01-02 | 0.001
    |    | 2003-01-02 | 0.002
(2 rows)

     dx     |  nx   |    dx1     |  nx1
------------+-------+------------+-------
 2000-01-02 | 0.005 |            |
            |       | 2002-01-02 | 0.001
            |       | 2003-01-02 | 0.002


Which isn't very pretty and doesn't really achieve what I want.

As I said "sql-writers block !"   ;-(

Tim


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