Re: PostgreSQL 10 parenthesized single-column updates can produce errors

On Tue, Oct 31, 2017 at 3:14 PM, Rob McColl <rob(at)robmccoll(dot)com> wrote:

>
>> I believe that this is not an intended change or behavior, but is instead
>> an unintentional side effect of 906bfcad7ba7cb3863fe0e2a7810be8e3cd84fbd
>> Improve handling of "UPDATE ... SET (column_list) = row_constructor". (
>> https://github.com/postgres/postgres/commit/906bfcad7ba7cb3
>> 863fe0e2a7810be8e3cd84fbd).
>>
>
​At this point the intent of 906bfcad doesn't really matter - and given the
number of complaints in the month since ​v10 went live I'm tending to lean
toward bringing the pre-10 behavior back. There is no ambiguity involved
here and the breakage of existing applications seems considerably worse
than the technical oddity of allowing (val) to be interpreted as a
row_constructor in this situation. From a standards perspective we are
strictly more permissive so no new problem there.

On a related note, the 10.0 syntax guide is wrong, it needs to break out
the parenthesized single-column and multi-column variants separately:

Presently: ( column_name [, ...] ) = [ ROW ] ( { expression | DEFAULT } [,
...] )

Basically one cannot specify only a single column_name AND omit ROW

It would have been nice if the syntax for that variant would have been:

( column_name, column_name [, ...] ) = [ ROW ] ( { expression | DEFAULT },
{ expression | DEFAULT } [, ...] )
​
If the v10 behavior remains the above change should be made as well as
adding:

( column_name ) = ROW ( expression | DEFAULT )

If we revert 10 to the pre-10 behavior the existing syntax will work.

David J.