Re: Row pattern recognition

Hi Jian and Tatsuo,

Thanks for the patch and the careful review.

Tatsuo, item 1 below (attribute notation inside a DEFINE clause) is a
question for you; the rest is feedback on Jian's patch.

> /* arity: a value expression and an optional offset */
> Typo: arity

"arity" may be an unfamiliar term, so I'll reword the comment in plainer
language ("takes a value expression and an optional offset").

> Simplify ParseFuncOrColumn:
> It now routes to ParseRPRNavCall exclusively when ParseExprKind is
> EXPR_KIND_RPR_DEFINE and not column projection and list_length(funcname)
> == 1. Original behavior is preserved otherwise.
> Centralize error handling:
> Treat RPR navigation as FUNCDETAIL_NORMAL to reuse the common error
> handling in ParseFuncOrColumn, effectively stripping redundant error
> checks from ParseRPRNavCall.

I'd take this structural part -- it's a clear cleanup: ParseRPRNavCall
drops the duplicated decoration checks while the common path gives the
identical messages, with no change in behavior or output.

Two user-visible changes in the patch I'd rather settle on their own
before taking them:

1. Attribute notation inside a DEFINE clause, e.g. (f).prev.

The guard this change removes is one I deliberately left undecided
during development (hence the XXX comment), so I'd keep it for now and
ask here. Without it, (f).prev with no such field gives a generic
"column \"prev\" not found ..." instead of the dedicated "cannot use
row pattern navigation function PREV in attribute notation". Three
options:

(a) Treat (f).prev as an ordinary function (prev(f)), the same as
outside a DEFINE clause -- which is what the patch does.

(b) Treat (f).prev as the navigation function -- read the attribute
notation as navigation. An ordinary function of that name is still
reachable as public.prev(...).

(c) Reject the ambiguous (f).prev with a dedicated error (what is
currently committed), rather than resolving it one way or the
other.

My own leaning is actually (a) -- it keeps attribute notation behaving
the same inside and outside a DEFINE clause. (c) is what's in the tree
now, and either way it changes the user-visible error and SQLSTATE, so
I'd rather settle this explicitly than let the refactor decide it
silently. Tatsuo, what do you think?

2. The offset type-mismatch message.

The patch rephrases

offset argument of %s must be type bigint, not type %s
to
%s offset argument of type %s cannot be coerced to the expected
bigint (+ a hint)

The behavior is identical, so I'd keep the original wording. "argument
... must be type X, not type Y" is the established phrasing -- it's what
coerce_to_boolean() produces, and the non-boolean DEFINE error in this
same feature already uses it. Rewording only the offset message would
be inconsistent with that, for no behavioral gain.

One small process note: for patches that aren't really being proposed to
the list yet -- ones still under review, or throwaway implementations
written just to analyze a problem -- could you send them off-list or as a
pull request instead? That keeps the thread focused on what's actually
being proposed for the patch.

Best regards,
Henson