commit 2bdd765f79df947b46a8b5a22e3b993b58cd6d32
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date:   Wed Sep 2 17:52:33 2009 +0000

    Fix subquery pullup to wrap a PlaceHolderVar around the entire RowExpr
    that's generated for a whole-row Var referencing the subquery, when the
    subquery is in the nullable side of an outer join.  The previous coding
    instead put PlaceHolderVars around the elements of the RowExpr.  The effect
    was that when the outer join made the subquery outputs go to null, the
    whole-row Var produced ROW(NULL,NULL,...) rather than just NULL.  There
    are arguments afoot about whether those things ought to be semantically
    indistinguishable, but for the moment they are not entirely so, and the
    planner needs to take care that its machinations preserve the difference.
    Per bug #5025.

    Making this feasible required refactoring ResolveNew() to allow more caller
    control over what is substituted for a Var.  I chose to make ResolveNew()
    a wrapper around a new general-purpose function replace_rte_variables().
    I also fixed the ancient bogosity that ResolveNew might fail to set
    a query's hasSubLinks field after inserting a SubLink in it.  Although
    all current callers make sure that happens anyway, we've had bugs of that
    sort before, and it seemed like a good time to install a proper solution.

    Back-patch to 8.4.  The problem can be demonstrated clear back to 8.0,
    but the fix would be too invasive in earlier branches; not to mention
    that people may be depending on the subtly-incorrect behavior.  The
    8.4 series is new enough that fixing this probably won't cause complaints,
    but it might in older branches.  Also, 8.4 shows the incorrect behavior
    in more cases than older branches do, because it is able to flatten
    subqueries in more cases.
Signed-off-by: NEkta Khanna <ekhanna@pivotal.io>