Re: Improving EXPLAIN's display of SubPlan nodes

On Tue, 19 Mar 2024 at 16:42, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Here's a hopefully-final version that makes that adjustment and
> tweaks a couple of comments.
>

This looks very good to me.

One final case that could possibly be improved is this one from aggregates.out:

explain (verbose, costs off)
select array(select sum(x+y) s
from generate_series(1,3) y group by y order by s)
from generate_series(1,3) x;
QUERY PLAN
-------------------------------------------------------------------
Function Scan on pg_catalog.generate_series x
Output: ARRAY(SubPlan 1)
Function Call: generate_series(1, 3)
SubPlan 1
-> Sort
Output: (sum((x.x + y.y))), y.y
Sort Key: (sum((x.x + y.y)))
-> HashAggregate
Output: sum((x.x + y.y)), y.y
Group Key: y.y
-> Function Scan on pg_catalog.generate_series y
Output: y.y
Function Call: generate_series(1, 3)

ARRAY operates on a SELECT with a single targetlist item, but in this
case it looks like the subplan output has 2 columns, which might
confuse people.

I wonder if we should output "ARRAY((SubPlan 1).col1)" to make it
clearer. Since ARRAY_SUBLINK is a special case, which always collects
the first column's values, we could just always output "col1" for
ARRAY.

Regards,
Dean