Re: Where's the doc for "array()" — as in "select array(values (17), (42))"
| От | Bryn Llewellyn |
|---|---|
| Тема | Re: Where's the doc for "array()" — as in "select array(values (17), (42))" |
| Дата | |
| Msg-id | FD968796-42C5-4FA1-AB61-66DD34049F79@yugabyte.com обсуждение исходный текст |
| Ответ на | Re: Re: Where's the doc for "array()" — as in "select array(values (17), (42))" (Tom Lane <tgl@sss.pgh.pa.us>) |
| Ответы |
Re: Where's the doc for "array()" — as in "select array(values (17), (42))"
Re: Re: Where's the doc for "array()" — as in "select array(values (17), (42))" |
| Список | pgsql-general |
tgl@sss.pgh.pa.us wrote:bryn@yugabyte.com wrote:Why is the "array()" constructor not found in "pg_proc"?Because it isn't a function. Yeah, it kind of looks like one, but its argument is a subquery. If SQL had first-class functions and closures, maybe ARRAY() could be implemented as an ordinary function. But I don't see any plausible way to do that as things stand.
There are a bunch of other things that look like functions but aren't in pg_proc, too :-(. Most of them are just catering to the SQL committee's weird allergy to writing functions with plain function syntax. But ARRAY()'s problem is semantic not syntactic.
There must be a significant difference between this:
select 'dog'
and this:
(select 'dog')
This works fine:
select length( (select 'dog') )
But without the doubled parentheses, it causes a syntax error.
On the other hand, an extra pair of surrounding parentheses here
select array( (values (17), (42)) )
while not necessary, *is* tolerated.
All this started because I had wrongly assumed that "pg_terminate_backend()" would have the same character as "array()" by not being subject to the "execute" privilege — just as is the case for all SQL built-ins in Oracle database, like "length()". I have a better mental model now.
Anyway, I know what to do in future. I'll simply look in pg_proc on a case-by-case basis.
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