Re: Query help

On 2019-01-26 18:04:23 -0500, Chuck Martin wrote:
> I'm having trouble formulating a query. This is a simplified version of the
> tables:
>
> ombcase
> ------------
> case_pkey integer, primary key
> casename varchar
> insdatetime timestamp w/o time zone
> status_fkey integer, foreign key
>
> status
> --------
> status_pkey integer, primary key
> statusid varchar
>
> statuschange
> --------
> statuschange_pkey integer, primary key
> insdatetime timestamp w/o time zone
> ombcase_fkey integer, foreign key
> oldstatus_fkey integer, foreign key
> newstatus_fkey integer, foreign key
> active integer, not nullable
>
> 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.

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(at)hjp(dot)at | management tools.
__/ | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>