> On 26 Mar 2015, at 1:25, Lavrenz, Steven M <slavr...@purdue.edu> wrote:
>
> Alright everyone, this is a doozy of a problem. I am new to Postgres so I
> appreciate patience/understanding. I have a database of hardware objects,
> each of which has several different “channels”. Once per day, these channels
> are supposed
>
>
>
> object_id channel check-in date
>
> ****************************************
>
> 990 1 2014-12-01
>
> 990 1 2014-12-02
>
> 990 2 2014-12-01
>
> 990 2 2014-12-02
>
> 286 2 2014-12-01
>
> 286 2 2014-12-02
>
> 286 5 2014-12-01
>
> 286 5 2014-12-02
>
> 4507 1 2014-12-01
>
> 4507 1 2014-12-02
>
> 4507 2 2014-12-01
>
> 4507 2 2014-12-02
>
>
>
> And so on. Occasionally, communications will break down to the hardware, such
> that no reporting occurs. object 286 loses communications on 12/1/2014. Then
> the table might look like:
>
>
>
> object_id channel check-in date
>
> ****************************************
>
> 990 1 2014-12-01
>
> 990 1 2014-12-02
>
> 990 2 2014-12-01
>
> 990 2 2014-12-02
>
>
>
> 286 2 2014-12-02
>
>
>
> 286 5 2014-12-02
>
> 4507 1 2014-12-01
>
> 4507 1 2014-12-02
>
> 4507 2 2014-12-01
>
> 4507 2 2014-12-02
>
>
>
> Or let’s say that for some reason, just channel 2 loses reporting for a day.
> Then we would have:
>
>
>
> object_id channel check-in date
>
> ****************************************
>
> 990 1 2014-12-01
>
> 990 1 2014-12-02
>
> 990 2 2014-12-01
>
> 990 2 2014-12-02
>
>
>
> 286 2 2014-12-02
>
> 286 5 2014-12-01
>
> 286 5 2014-12-02
>
> 4507 1 2014-12-01
>
> 4507 1 2014-12-02
>
> 4507 2 2014-12-01
>
> 4507 2 2014-12-02
>
>
>
> I have a second table (TABLE B) with all of the object_ids and channels that
> are supposed to be reporting in each day. For cases where a certain channel
> does not check in, I want to add a column that indicates the comm failure.
> So, for
>
>
>
> object_id channel check-in date
> comm failure
>
> **********************************************************
>
> 990 1 2014-12-01
> No
>
> 990 1 2014-12-02
> No
>
> 990 2 2014-12-01
> No
>
> 990 2 2014-12-02
> No
>
> 286 2 2014-12-01
> Yes
>
> 286 2 2014-12-02
> No
>
> 286 5 2014-12-01
> Yes
>
> 286 5 2014-12-02
> No
>
> 4507 1 2014-12-01
> No
>
> 4507 1 2014-12-02
> No
>
> 4507 2 2014-12-01
> No
>
> 4507 2 2014-12-02
> No
>
>
>
>
>
> I have been racking my mind for the better part of a day on how to do this.
> The thing is that I can do a right join of TABLE B on TABLE A, and this will
> populate the missing object ids and channels. However, this only works for a
> single
>
>
>
> object_id channel check-in date
> comm failure
>
> **********************************************************
>
> 990 1 2014-12-01
> No
>
> 990 1 2014-12-02
> No
>
> 990 2 2014-12-01
> No
>
> 990 2 2014-12-02
> No
>
> 286 2
> Yes
>
> 286 2 2014-12-02
> No
>
> 286 5
> Yes
>
> 286 5 2014-12-02
> No
>
> 4507 1 2014-12-01
> No
>
> 4507 1 2014-12-02
> No
>
> 4507 2 2014-12-01
> No
>
> 4507 2 2014-12-02
> No
>
>
>
> I need to do a count of comm failures by day, so I need to populate the
> check-in date field. Please help!
Easiest would be to insert the missing values in your table, something like:
WITH RECURSIVE calendar (missing_date) AS (
SELECT MAX(check_in_date) FROM table_a WHERE comm_failure = 'YES'
UNION ALL
SELECT missing_date + interval '1 day' FROM calendar
WHERE missing_date < CURRENT_DATE
)
INSERT INTO table_a (object_id, channel, check_in_date, comm_failure)
SELECT b.object_id, b.channel. c.missing_date, 'YES'
FROM table_b b, calendar c
WHERE NOT EXISTS (
SELECT 1
FROM table_a a
WHERE a.object_id = b.object_id
AND a.channel = b.channel
AND a.check_in_date = c.missing_date
);
That's off the top of my head, untested, etc, but I think I got that mostly
right.
Alban Hertroys
--
If you can't see the forest for the trees,
cut the trees and you'll find there is no forest.
--
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