Fix up planner infrastructure to support LATERAL properly.

This patch takes care of a number of problems having to do with failure
to choose valid join orders and incorrect handling of lateral references
pulled up from subqueries.  Notable changes:

* Add a LateralJoinInfo data structure similar to SpecialJoinInfo, to
represent join ordering constraints created by lateral references.
(I first considered extending the SpecialJoinInfo structure, but the
semantics are different enough that a separate data structure seems
better.)  Extend join_is_legal() and related functions to prevent trying
to form unworkable joins, and to ensure that we will consider joins that
satisfy lateral references even if the joins would be clauseless.

* Fill in the infrastructure needed for the last few types of relation scan
paths to support parameterization.  We'd have wanted this eventually
anyway, but it is necessary now because a relation that gets pulled up out
of a UNION ALL subquery may acquire a reltargetlist containing lateral
references, meaning that its paths *have* to be parameterized whether or
not we have any code that can push join quals down into the scan.

* Compute data about lateral references early in query_planner(), and save
in RelOptInfo nodes, to avoid repetitive calculations later.

* Assorted corner-case bug fixes.

There's probably still some bugs left, but this is a lot closer to being
real than it was before.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/backend/optimizer/util/placeholder.c b/src/backend/optimizer/util/placeholder.c
index e05c8ddef1b..317a01940e3 100644
--- a/src/backend/optimizer/util/placeholder.c
+++ b/src/backend/optimizer/util/placeholder.c
@@ -412,14 +412,14 @@ add_placeholders_to_base_rels(PlannerInfo *root)
 		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
 		Relids		eval_at = phinfo->ph_eval_at;
 
-		if (bms_membership(eval_at) == BMS_SINGLETON)
+		if (bms_membership(eval_at) == BMS_SINGLETON &&
+			bms_nonempty_difference(phinfo->ph_needed, eval_at))
 		{
 			int			varno = bms_singleton_member(eval_at);
 			RelOptInfo *rel = find_base_rel(root, varno);
 
-			if (bms_nonempty_difference(phinfo->ph_needed, rel->relids))
-				rel->reltargetlist = lappend(rel->reltargetlist,
-											 copyObject(phinfo->ph_var));
+			rel->reltargetlist = lappend(rel->reltargetlist,
+										 copyObject(phinfo->ph_var));
 		}
 	}
 }