tgl@sss.pgh.pa.us wrote:
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:
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.