Re: pg_plan_advice

Here's v7.

In 0001, I removed "const" from a node's struct declaration, because
Tom gave me some feedback to avoid that on another recent patch, and I
noticed I had done it here also. 0002, 0003, and 0004 are unchanged.

In 0005:

- Refactored the code to avoid issuing SEMIJOIN_NON_UNIQUE() advice in
cases where uniqueness wasn't actually considered.
- Adjusted the code not to issue NO_GATHER() advice for non-relation
RTEs. (This is the issue reported by Ajay Pal in a recent message to
this thread, which was also mentioned in an XXX in the code.)
- Reject zero-length delimited identifiers, per Jacob's email.
- Properly initialize element->indexes in pgpa_trove_add_to_hash, per
Jacob'e email.
- Add gather((d d/d.d)) test case, per Jacob, and fix the related bug
in pgpa_identifier_matches_target, per Jacob's email.
- Add EXPLAIN SELECT 1 after various test cases in syntax.sql, to
improve test coverage, per analysis of why the existing test case
didn't catch a bug previously reported by Jacob.
- Added a dummy initialization to pgpa_collector.c to placate nervous
compilers, per discussion with Jacob.

I think this mostly catches me up on responding to issues reported
here, although there is one thing reported to me off-list that I
haven't dealt with yet. If there's anything reported on thread that
isn't addressed here, let me know.

Thanks,

--
Robert Haas
EDB: http://www.enterprisedb.com