Re: patch: function xmltable

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: Craig Ringer <craig(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: patch: function xmltable
Date: 2016-12-07 17:34:59
Message-ID: 20161207173459.hv7cltspcjnvj732@alvherre.pgsql
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Pavel Stehule wrote:

> I fixed two issues.
> 2. there was reverse setting in NOT NULL flag

Ah-hah, that was silly, thanks.

> 1. there are not columns data when there are not any explicit column - fixed

Hmm. Now that I see how this works, by having the GetValue "guess" what
is going on and have a special case for it, I actually don't like it
very much. It seems way too magical. I think we should do away with
the "if column is NULL" case in GetValue, and instead inject a column
during transformTableExpr if columns is NIL. This has implications on
ExecInitExpr too, which currently checks for an empty column list -- it
would no longer have to do so.

Maybe this means we need an additional method, which would request "the
expr that returns the whole row", so that transformExpr can work for
XmlTable (which I think would be something like "./") and the future
JsonTable stuff (I don't know how that one would work, but I assume it's
not necessarily the same thing).

Álvaro Herrera
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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