如何按计划更新PostgreSQL表中的值？

Question

Let's say I have a vet application, and there're 2 databases(let's say doctors perform operations):

User database with fields : id, email, name, password and regStamp.

PetOperations database with fields: id, id(reference to user), doctorName, operationStamp and operationStatus.

What if I want to update a operationStatus field whenever someone puts a new petOperation in Pet database(initial status was PERFOMING after 20 minutes it becomes PERFORMED, but only for this unique operationId, if currentTime - operationStamp >=20). How can I do that? Maybe, there's a better way rather than subtraction times?

Answer 1

I think you need to rethink your data model a little bit. As I understand your question you have operations which are scheduled, and you want to treat them as performed after the scheduled time slice is complete.

PostgreSQL has no native facility to update a value in 20 minutes. You could use a cron job, but I think the more elegant solution is to change your data model instead.

Add a "table method" and you get status calculation.

suppose your table now contains:

id, id(reference to user), doctorName, operationStamp, operationTsrange

Then you create a function something like:

create or replace function status(operation) returns text language sql
as $$
     select case when $1.operationTsrange is null then 'Not Scheduled'
                 when now() << $1.operationTsrange THEN 'Scheduled'
                 when now() <@ $1.operationTsrange THEN 'Performing'
                 when now() >> $1.operationTsrange THEN 'Performed'
             END;
$$;

Then you can search on this. And if you need different length intervals you can specify them on update time.

Answer 2

I am not sure what you want to do.

If you just want to set the initial operationstatus when you INSERT a row, use a BEFORE INSERT trigger.

If you want the value to change depending on when it is selected, use a “computed column”, that is, don't define the column in the table, but rather define a view on the table that contains the column, calculated as appropriate.