Re: Make subquery alias optional in FROM clause

On 22 February 2017 at 15:08, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Indeed. When I wrote the comment you're referring to, quite a few years
> ago now, I thought that popular demand might force us to allow omitted
> aliases. But the demand never materialized. At this point it seems
> clear to me that there isn't really good reason to exceed the spec here.
> It just encourages people to write unportable SQL code.

Oh my. This bothers me all the time. I always assumed the reason it
was like this was because the grammar would be ambiguous without it
and it would require extreme measures to hack the grammar to work. If
it's this easy I would totally be for it.

Offhand I think there are plenty of solutions for the problem of
inventing names and I suspect any of them would work fine:

1) Don't assign a name -- I would guess this would require some
adjustments in the rule deparsing (i.e. views).

2) Assign a name but add a flag indicating the name is autogenerated
and shouldn't be used for resolving references and shouldn't be
dumped. Then it shouldn't really matter if there's a conflict since
the name is only used for things like error messages, not resolving
references.

3) thumb through all the names in the query and pick one that doesn't conflict.

For what it's worth while it wouldn't be a *bad* thing to avoid
conflicts I think this is being held to an inconsistent standard here.
It's not like there aren't similar situations elsewhere in the
codebase where we just don't worry about this kind of thing:

=> SELECT "?column"? FROM (select 1+1 as "?column?", 1+1) AS x;
ERROR: 42703: column "?column" does not exist
LINE 2: SELECT "?column"? FROM (select 1+1 as "?column?", 1+1) AS x;
^
HINT: Perhaps you meant to reference the column "x.?column?" or the
column "x.?column?".

--
greg