Re: Early WIP/PoC for inlining CTEs

I wrote:
> I propose that we implement and document this as
> 	WITH ctename AS [ MATERIALIZE { ON | OFF } ] ( query )
> which is maybe a bit clunky but not awful, and it would leave room
> to generalize it to "AS [ optionname optionvalue [ , ... ] ]" if we
> ever need to.  Looking at the precedent of e.g. EXPLAIN, we could
> probably allow just "MATERIALIZE" as well, with the boolean value
> defaulting to true.

In hopes of moving things along, here's a version of the patch that
does it like that.  This demonstrates that, in fact, we can accept
"keyword [value] [, ...]" style options without any parens and
there's no syntax conflict.  We'd have to work a bit harder on the
actual code in gram.y if we wanted to handle multiple options,
but the Bison productions will work.

There's nothing particularly stopping us from accepting
"materialized" with a D in this syntax, instead of or in addition
to "materialize"; though I hesitate to mention it for fear of
another round of bikeshedding.

After further reflection I really don't like Andrew's suggestion
that we not document the rule that multiply-referenced CTEs won't
be inlined by default.  That would be giving up the principle
that WITH calculations are not done multiple times by default,
and I draw the line at that.  It's an often-useful behavior as
well as one that's been documented from day one, so I do not accept
the argument that we might someday override it on the basis of
nothing but planner cost estimates.

			regards, tom lane