From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "Hitoshi Harada" <umi(dot)tanuki(at)gmail(dot)com> |
Cc: | "Heikki Linnakangas" <heikki(dot)linnakangas(at)enterprisedb(dot)com>, "David Rowley" <dgrowley(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Windowing Function Patch Review -> Standard Conformance |
Date: | 2008-12-21 20:21:36 |
Message-ID: | 6363.1229890896@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
I wrote:
> I've been hacking on this and I have a grammar that pretty much works,
> but there's some bizarreness around UNBOUNDED. I'll post it later.
Here is a proof-of-concept grammar patch that allows frame_bound to use
a_expr instead of a hacked-up constant production (which, as I
complained before, didn't allow all the cases demanded by the spec).
The key changes involved are:
* BETWEEN has to become a fully reserved word instead of type_func_name.
* PARTITION RANGE ROWS FOLLOWING PRECEDING have to be assigned the same
explicit precedence as IDENT. (This doesn't have any bad consequences
AFAIK, except that you can't use a postfix operator in frame_bound exprs
unless you parenthesize it.)
* UNBOUNDED has to be assigned a precedence slightly lower than
PRECEDING and FOLLOWING, else it's ambiguous whether "UNBOUNDED
PRECEDING" ought to be parsed as "a_expr PRECEDING". I'm a bit nervous
about this solution; we might someday need to make some of these
keywords at least partly reserved instead. But right now it doesn't
seem to have any negative consequences.
Making BETWEEN fully reserved is a bit annoying, but it would only
break apps using BETWEEN as a type or function name. The former doesn't
seem like a problem, the latter might be.
Comments?
regards, tom lane
PS: I've removed some uninteresting hunks to shorten the diff, so you might
get some chatter from patch if you try to apply the diff.
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