Re: [HACKERS] PostgreSQL 10 parenthesized single-column updates canproduce errors

От

David G. Johnston

Тема

Дата

1 ноября 2017 г. в 01:45:28

Msg-id

CAKFQuwZcht7u6eV6CUFFw3unGphasTL5-Wce5NwPnekhw-vDtg@mail.gmail.com

обсуждение

Ответ на

Re: [HACKERS] PostgreSQL 10 parenthesized single-column updates can produce errors (Rob McColl)

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pgsql-hackers

Дерево обсуждения

Re: [HACKERS] PostgreSQL 10 parenthesized single-column updates can produce errors Tom Lane <tgl@sss.pgh.pa.us> 1 ноября 2017 г. в 01:43:59

Re: [HACKERS] PostgreSQL 10 parenthesized single-column updates canproduce errors "David G. Johnston" <david.g.johnston@gmail.com> 1 ноября 2017 г. в 01:48:39

Re: [HACKERS] PostgreSQL 10 parenthesized single-column updates can produce errors Tom Lane <tgl@sss.pgh.pa.us> 1 ноября 2017 г. в 02:05:38

On Tue, Oct 31, 2017 at 3:14 PM, Rob McColl <rob@robmccoll.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/906bfcad7ba7cb3863fe0e2a7810be8e3cd84fbd).

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.

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