Without the STREAM keyword it's clear, it's the old-fashioned SQL, no issue
there.
I'm interested in the STREAM case. My question is, if you use the STREAM
keyword (either after SELECT or at the end), which of the tables is treated
as a stream? Order_item, product or both?
Viliam
On Fri, 20 Mar 2020 at 21:30, Julian Hyde <jh...@apache.org> wrote:
> I should have said that
>
> SELECT * FROM order_item o JOIN product p USING(product_id)
>
> (without the "STREAM" keyword) is a time-varying relation. You can
> execute it at 10am, and it terminates, and again at 10.10am and get
> different results. The difference is due to differences in both
> product and order_item.
>
> If you want to join based on when the order was placed, you must have
> a column that records the order time. Beyond that, I'm not sure of the
> details - you may be able to use AS OF, there may be a
> system-maintained column that records when product was last updated.
>
> Julian
>
> On Fri, Mar 20, 2020 at 12:01 AM Viliam Durina <vil...@hazelcast.com>
> wrote:
> >
> > On Thu, 19 Mar 2020 at 21:04, Julian Hyde <jh...@apache.org> wrote:
> >
> > Suppose you execute that query at 10am and get a particular result. ...
> you
> > > execute again at 10.10am.
> > >
> >
> > I execute that query at 10am and expect it to run continuously. My
> > understanding is that a query with `EMIT STREAM` will run continuously.
> > Does it just fetch results and finish?
> >
> > Now, if you have particular time-sensitive join semantics - such as
> wanting
> > > to join the order_item to the product table as if was at the time the
> order
> > > was placed - you will need to express that explicitly in the join
> condition.
> > >
> >
> > How would such a query look? Could you write it? There's no time column
> in
> > either relation.
> >
> > Regards,
> > Viliam
> >
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