Tom Lane wrote:
Dennis Haney <davh@diku.dk> writes:

As far as I can tell, the pull_up_IN_clauses does not optimize
recursively. Am I totally misguided here?
Yes. The subquery is not being physically folded into the outer query
(so the comment about "pulling up" may be a poor choice of words).
It will still get planned separately by a recursive call to
subquery_planner, and any internal INs will get fixed at that time.

It is possible and even rather likely that the subsequent run of
pull_up_subqueries will flatten the subquery into the outer query,
and if so its internal INs are fixed during pull_up_subqueries.
But doing it here would be redundant.
I think I figured it out now, after looking at it for hours...

I saw it as though convert_IN_to_join rewrote the query from

select a.* from tenk1 a where a.unique1 in
(select c.thousand from tenk1 c where c.hundred = 99);

to

select a.* from tenk1 a, tenk1 c where a.unique1 = c.thousand AND
c.hundred = 99;

But after looking at it, I've reached the conclusion that the rewrite is
to this instead:

select a.* from tenk1 a, (select d.thousand from tenk1 d where
d.hundred = 99) as c where a.unique1 = c.thousand;

except the subselect is added as a range table entry instead of a
subselect in the from-list (not that I understand this particular part,
do you mind explaining?).

Or am I still totally lost?

--
Dennis

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postedJan 20, '04 at 3:25p
activeJan 23, '04 at 5:53p
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