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, 21 insertions, 0 deletions

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 5abb114ba8e..6917ee55aa6 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -298,6 +298,7 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 	List	   *joininfos;
 	Index		rti;
 	ListCell   *l;
+	ListCell   *nextl;
 
 	/*
 	 * Mark the rel as "dead" to show it is no longer part of the join tree.
@@ -351,6 +352,26 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 	}
 
 	/*
+	 * Likewise remove references from LateralJoinInfo data structures.
+	 *
+	 * If we are deleting a LATERAL subquery, we can forget its
+	 * LateralJoinInfo altogether.  Otherwise, make sure the target is not
+	 * included in any lateral_lhs set.  (It probably can't be, since that
+	 * should have precluded deciding to remove it; but let's cope anyway.)
+	 */
+	for (l = list_head(root->lateral_info_list); l != NULL; l = nextl)
+	{
+		LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(l);
+
+		nextl = lnext(l);
+		if (ljinfo->lateral_rhs == relid)
+			root->lateral_info_list = list_delete_ptr(root->lateral_info_list,
+													  ljinfo);
+		else
+			ljinfo->lateral_lhs = bms_del_member(ljinfo->lateral_lhs, relid);
+	}
+
+	/*
 	 * Likewise remove references from PlaceHolderVar data structures.
 	 *
 	 * Here we have a special case: if a PHV's eval_at set is just the target