Re: Query help - Mailing list pgsql-general
| From | Chuck Martin |
|---|---|
| Subject | Re: Query help |
| Date | |
| Msg-id | CAFw6=U3ENYoeQEfwndgRWvrUe0VgL4Q4ajuRt=0qp8CSYoER-w@mail.gmail.com Whole thread Raw |
| In response to | Re: Query help ("Peter J. Holzer" <hjp-pgsql@hjp.at>) |
| Responses |
Re: Query help
|
| List | pgsql-general |
On Sun, Jan 27, 2019 at 8:07 AM Peter J. Holzer <hjp-pgsql@hjp.at> wrote:
On 2019-01-26 18:04:23 -0500, Chuck Martin wrote:
[snip]
> The idea should be obvious, but to explain, insdatetime is set when a new
> record is created in any table. All records in ombcase have a foreign key to
> status that can't be null. When status changes, a record is created in
> statuschange recording the old and new status keys, and the time (etc).
>
> The goal is to find records in ombcase that have not had a status change in xx
> days. If the status has not changed, there will be no statuschange record.
The easiest way is to use set operations:
select case_pkey from ombcase;
gives you all the ombcase ids.
select ombcase_fkey from statuschange where insdatetime >= now()::date - xx;
gives you all ombcase ids which had a status change in the last xx days.
Therefore,
select case_pkey from ombcase
except
select ombcase_fkey from statuschange where insdatetime >= now()::date - xx;
gives you all ombcase ids which did /not/ have a status change in the
last xx days.
I was not familiar with set operations, but studied up a bit and thought I was getting there. Not quite, though. I have two queries that individually return 1) all ombcase records with no statuschange record, and 2) the newest statuschange record for each case that has a statuschange record. But just putting UNION between then doesn't work. Here are my queries:
--First, find all open cases with no statuschange record
SELECT
case_pkey,statuschange_pkey,case_fkey,ombcase.insdatetime,statuschange.insdatetime
FROM
ombcase
LEFT JOIN
statuschange
ON
statuschange.case_fkey = case_pkey
AND case_pkey <> 0
LEFT JOIN
status
ON status_fkey = status_pkey
WHERE lower(statusid) NOT LIKE ('closed%')
AND statuschange.statuschange_pkey IS NULL
UNION
--Now find the last status change record for each case that has one
SELECT DISTINCT ON (case_fkey)
case_pkey,statuschange_pkey,case_fkey,ombcase.insdatetime,statuschange.insdatetime
FROM
statuschange,ombcase,status
WHERE case_fkey = case_pkey
AND status_fkey = status_pkey
AND LOWER(statusid) NOT LIKE ('closed%')
ORDER BY case_fkey, statuschange.insdatetime DESC
If I run each part separately, I get the expected number of records. When I combine them with UNION, I get "missing FROM-clause entry for table "statuschange" So I'm very close here, and these two return the exact number of records I'm expecting. So I just need to get them added together. Then I expect I can put the whole thing in a WHERE clause with "AND ombcase.case_pkey IN ([the combined results])"
Another way would be to use a CTE
(https://www.postgresql.org/docs/10/queries-with.html) to extract the
last status change for each ombcase and then do a left join of ombcase
to that CTE.
hp
--
_ | Peter J. Holzer | we build much bigger, better disasters now
|_|_) | | because we have much more sophisticated
| | | hjp@hjp.at | management tools.
__/ | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>
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