Re: Proposition for autoname columns
| От | David G. Johnston |
|---|---|
| Тема | Re: Proposition for autoname columns |
| Дата | |
| Msg-id | CAKFQuwbChHdQFVN2LEJNm=iUyCRtepmDdpUKgF4NK03ecnXXww@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Proposition for autoname columns (Andrew Dunstan <andrew@dunslane.net>) |
| Ответы |
Re: Proposition for autoname columns
|
| Список | pgsql-hackers |
On Thu, Nov 12, 2020 at 9:32 AM Andrew Dunstan <andrew@dunslane.net> wrote:
On 11/12/20 11:12 AM, David G. Johnston wrote:
> On Thu, Nov 12, 2020 at 8:59 AM Andrew Dunstan <andrew@dunslane.net
> <mailto:andrew@dunslane.net>> wrote:
>
>
>
> So if we then say:
>
>
> select x, j->>x from mytable;
>
>
> you want both result columns named x? That seems like a recipe for
> serious confusion. I really don't think this proposal has been
> properly
> thought through.
>
>
> IMO It no worse than today's:
>
> select count(*), count(*) from (values (1), (2)) vals (v);
> count | count
> 2 | 2
>
I guess the difference here is that there's an extra level of
indirection. So
select x, j->>'x', j->>x from mytable
would have 3 result columns all named x.
I totally missed the variable reference there - only two of those become "x", the variable reference stays un-rewritten and thus results in "?column?", similar to today:
select count(*), count(*) +1 from (values (1), (2)) vals (v);
count | ?column?
2 | 2
The query rewriter would only rewrite these expressions and provide an expression-related explicit alias clause if the expression is a single operator (same as single function today) and the right-hand side of the operator is a constant (meaning the constant is a reasonable representation of every output value that is going to appear in the result column). If the RHS is a variable then there is no good name that is known to cover all output values and thus ?column? (i.e., do not rewrite/provide an alias clause) is an appropriate choice.
My concerns in this area involve stored views and ruleutils, dump/reload by extension. Greenfield, this would have been nice, and worth the minimal complexity given its usefulness in the common case, but is it useful enough to introduce a whole new default naming mechanism and dealing with dump/restore concerns?
David J.
В списке pgsql-hackers по дате отправления: