Re: Multiple-Table-Spanning Joins with ORs in WHERE Clause

On 29.09.2016 22:26, Jeff Janes wrote:
> Well, I don't recall seeing this issue on this list before (or a few
> other forums I read) while I see several other issues over and over
> again. So that is why I think it is a niche issue. Perhaps I've have
> seen it before and just forgotten, or have not recognized it as being
> the same issue each time.

Understood.

>
> This multitude of solution also shows that applications developers
> might be overwhelmed by choosing the most appropriate AND most
> long-lasting one. Because what I take from the discussion is that
> a UNION might be appropriate right now but that could change in
> the future even for the very same use-case at hand.
>
>
> I'm not sure what would cause it to change. Do you mean if you
> suddenly start selecting a much larger portion of the table? I don't
> know that the union would be particularly bad in that case, either.

Not suddenly but gradually. Data can change and we don't know for sure
how people will use our systems in the future. Hence, another plan would
be more optimal or even a seq scan on big_table would be faster.

In the case at hand, I doubt it but you never know.

> I'm not saying it wouldn't be nice to fix it. I just don't think it
> is particularly likely to happen soon. I could be wrong (especially
> if you can write the code to make it happen).

I have been thinking about this. It would be an interesting exercise as
I haven't written much of C in the last decade but sometimes one needs
to get out of the comfort zone to get things going.

Sven