On 2016/12/07 15:39, Ashutosh Bapat wrote:

On 2016/11/22 18:28, Ashutosh Bapat wrote:

I guess, the reason why you are doing it this way, is SELECT clause for
outermost query gets deparsed before FROM clause. For later we call
deparseRangeTblRef(), which builds the tlist. So, while deparsing SELECT
clause, we do not have tlist to build from. In that case, I guess, we have
build the tlist in get_subselect_alias_id() if it's not available and
stick it
in fpinfo. Subsequent calls to get_subselect_alias_id() should find tlist
there. Then in deparseRangeTblRef() assert that there's a tlist in fpinfo
and use it to build the SELECT clause of subquery. That way, we don't
tlist unless it's needed and also use the same tlist for all searches.
use tlist_member() to search into the tlist.

I wrote:
This would probably work, but seems to me a bit complicated.  Instead, I'd
like to propose that we build the tlist for each relation being deparsed as
a subquery in a given join tree, right before deparsing the SELECT clause in
deparseSelectStmtForRel, if is_subquery is false and lower_subquery_rels
isn't NULL, and store the tlist into the relation's fpinfo.  That would
allow us to build the tlist only when we need it, and to use tlist_member
for the exact comparison.  I think it would be much easier to implement

IIRC, this is inline with my original proposal of creating tlists
before deparsing anything. Along-with that I also proposed to bubble
this array of tlist up the join hierarchy to avoid recursion [1] point
#15, further elaborated in [2]


We seem to be moving towards that solution, but as discussed we have
left it to committer's judgement.

My proposal here would be a bit different from what you proposed; right before deparseSelectSql in deparseSelectStmtForRel, build the tlists for relations present in the given jointree that will be deparsed as subqueries, by (1) traversing the given jointree and (2) applying build_tlist_to_deparse to each relation to be deparsed as a subquery and saving the result in that relation's fpinfo. I think that would be implemented easily, and the overhead would be small.

Best regards,
Etsuro Fujita

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