Re: BUG #14573: lateral joins, ambuiguity

On Wednesday, March 1, 2017, <dlw405(at)gmail(dot)com> wrote:

> The following bug has been logged on the website:
>
> Bug reference: 14573
> Logged by: Denise Wiedl
> Email address: dlw405(at)gmail(dot)com
> PostgreSQL version: 9.5.3
> Operating system: osx 10.11.5
> Description:
>
> PostgreSQL 9.5.3 on x86_64-apple-darwin15.4.0, compiled by Apple LLVM
> version 7.3.0 (clang-703.0.31), 64-bit
>
> The LATERAL JOIN has access to all previous columns in the join, but, it
> doesn't give an error when there are two columns of the same name. Instead,
> it silently selects the first column.
>
> LEFT JOIN LATERAL (
> SELECT "1".*, owner
> FROM banana "1"
> LEFT JOIN LATERAL (
> SELECT "2".*
> FROM users "2"
> WHERE "1".owner_id = "2".id
> ) owner
>

IIUC the preference exhibited is an explicit column present on the left
side of the join over the implicit relation named column within its own
query.

​Simpler self-contained example:

select *
from (values (1)) vals (v)
left join lateral (
select v
from (values (2)) v (val)
) src on (true)

Returns (1,1) instead of the desired (1,(2))

​Beyond my pay grade for diagnostics. I don't recall this being documented
and I haven't looked for it yet.

If I come up with a non-lateral involved example before this is answered
I'll come back and post it.

David J.