Fix nested PlaceHolderVar expressions that appear only in targetlists.

A PlaceHolderVar's expression might contain another, lower-level
PlaceHolderVar.  If the outer PlaceHolderVar is used, the inner one
certainly will be also, and so we have to make sure that both of them get
into the placeholder_list with correct ph_may_need values during the
initial pre-scan of the query (before deconstruct_jointree starts).
We did this correctly for PlaceHolderVars appearing in the query quals,
but overlooked the issue for those appearing in the top-level targetlist;
with the result that nested placeholders referenced only in the targetlist
did not work correctly, as illustrated in bug #6154.

While at it, add some error checking to find_placeholder_info to ensure
that we don't try to create new placeholders after it's too late to do so;
they have to all be created before deconstruct_jointree starts.

Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index bb38768bd43..1b264a29e29 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -3491,7 +3491,7 @@ set_rel_width(PlannerInfo *root, RelOptInfo *rel)
 		else if (IsA(node, PlaceHolderVar))
 		{
 			PlaceHolderVar *phv = (PlaceHolderVar *) node;
-			PlaceHolderInfo *phinfo = find_placeholder_info(root, phv);
+			PlaceHolderInfo *phinfo = find_placeholder_info(root, phv, false);
 
 			tuple_width += phinfo->ph_width;
 		}