Re: explain and PARAM_EXEC

Tom Lane wrote:
> Anyway, I hadn't looked at your patch before, but now that I have, it's
> not even approximately what I was suggesting. What I thought you should
> do was change ruleutils.c to print the parameter expressions at the call
> site, ie in the T_SubPlan and T_AlternativeSubPlan cases in get_rule_expr.
>
See patch below against HEAD.

Example of query against catalog:

postgres=# explain verbose select oid::int + 1,(select oid from pg_class
a where a.oid = b.relfilenode and a.relnamespace = b.relnamespace) from
pg_class b;
QUERY
PLAN
--------------------------------------------------------------------------------------------------------
Seq Scan on pg_catalog.pg_class b (cost=0.00..2459.64 rows=296 width=12)
Output: ((b.oid)::integer + 1), SubPlan 1 ($0 := b.relfilenode, $1 :=
b.relnamespace)
SubPlan 1
-> Index Scan using pg_class_oid_index on pg_catalog.pg_class a
(cost=0.00..8.27 rows=1 width=4)
Output: a.oid
Index Cond: (a.oid = $0)
Filter: (a.relnamespace = $1)
(7 rows)

Explain of alternative subplan (query comes from aggregates.sql in
regression).

regression=# explain verbose select ten, sum(distinct four) from onek a
group by ten
having exists (select 1 from onek b where sum(distinct a.four) = b.four);
QUERY
PLAN
--------------------------------------------------------------------------------------
GroupAggregate (cost=197.83..216.52 rows=10 width=8)
Output: a.ten, sum(DISTINCT a.four)
Filter: (alternatives: SubPlan 1 ($0 := sum(DISTINCT a.four)) or
hashed SubPlan 2)
-> Sort (cost=197.83..200.33 rows=1000 width=8)
Output: a.ten, a.four
Sort Key: a.ten
-> Seq Scan on public.onek a (cost=0.00..148.00 rows=1000
width=8)
Output: a.ten, a.four
SubPlan 1
-> Seq Scan on public.onek b (cost=0.00..150.50 rows=250 width=0)
Filter: ($0 = b.four)
SubPlan 2
-> Seq Scan on public.onek b (cost=0.00..148.00 rows=1000 width=4)
Output: b.four
(14 rows)

Would the explain above be better if the filter with subplans arguments
showed the EXISTS keyword? Much code from get_sublink_expr could be
reused to show additional info depending on the sublink type and testexpr.

Other info: there are now only appends to the context->buf. The problems
with OUTER var I mentioned earlier are gone now arguments are deparsed
using get_rule_expr instead of deparse_expression.

regards,
Yeb Havinga