Re: Query help - Mailing 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])"