Re: issue: record or row variable cannot be part of multiple-item INTO list

On Sat, May 13, 2017 at 4:20 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> IIRC, the reason for disallowing that is that it's totally unclear what
> the semantics ought to be. Is that variable a single target (demanding
> a compatible composite-valued column from the source query), or does it
> eat one source column per field within the record/row? The former is 100%
> inconsistent with what happens if the record/row is the only INTO target;
> while the latter would be very bug-prone, and it's especially unclear what
> ought to happen if it's an as-yet-undefined record variable.

Maybe I'm just confused here, but do you think that anyone at all
wants the second behavior?

I think the fact that single-target INTO lists and multiple-target
INTO lists are handled completely differently is extremely poor
language design. It would have been far better, as you suggested
downthread, to have added some syntax up front to let people select
the behavior that they want, but I think there's little hope of
changing this now without creating even more pain.

I have a really hard time, however, imagining that anyone writes
SELECT a, b, c, d, e, f, g, h, i, j, k INTO x, y, z and wants some of
a-k to go into x, some more to go into y, and some more to go into z
(and heaven help you if you drop a column from x or y -- now the whole
semantics of the query change, yikes). What's reasonable is to write
SELECT a, b, c INTO x, y, z and have those correspond 1:1.

--
Robert Haas
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