Re: BUG #16212: subquery block allows to overwrite table alias defined earlier

On Thu, Jan 16, 2020 at 3:37 PM PG Bug reporting form <
noreply(at)postgresql(dot)org> wrote:

> The following bug has been logged on the website:
>
> Bug reference: 16212
> Logged by: Denis Girko
> Email address: luza(dot)mbox(at)gmail(dot)com
> PostgreSQL version: 9.6.16
> Operating system: Linux
> Description:
>

These are just examples of poorly written queries where sub-query
correlated value injection results in an arbitrary edge case: specifically,
when a query can resolve a name as either a column or a table it chooses
the column. Your choice of encoding your expected and actual output
doesn't help you here as you are not distinguishing between a scalar column
result and a composite table result being present.

select a from (values(1)) a; -- yields (1); the parens denote the result is
a composite with a single field (whose name is "column1" since it was not
given a name explicitly)
select a from (values(1)) a (a); -- yields 1; no parens denote the scalar
result of 1 since the column named "a" exists and is preferred over the
table named "a"

David J.