Re: Hey! ORDER BY in VIEWS?

"Josh Berkus" <josh(at)agliodbs(dot)com> writes:
>> Hmm, I just realized that there's a bug here: let's say you have
>>
>> CREATE VIEW latest AS
>> SELECT * FROM news ORDER BY story_timestamp DESC LIMIT 1;
>>
>> ie, this view gives you the latest news story.

> Why, exactly, do we need to support ORDER BY ... LIMIT in VIEWS, anyway?
> I'm frankly unclear on the utility of this ...

I think the above example is pretty compelling, don't you? Easy to read
and it generates a very nice indexscan plan.

> If we gotta have 'em, though, Tom, you'd have to code in an exception to
> the VIEW optimizer that doesn't push down WHERE clauses if the VIEW has
> an ORDER BY ... LIMIT statement. Sure you wanna get into this?

It's a one-line addition to code that already knows that certain kinds
of clauses (like UNION) prevent pushdown. Just an oversight, not a
fundamental flaw.

regards, tom lane