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, 9 insertions, 0 deletions

diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index 9838dc45d5e..04acc006f53 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -141,6 +141,7 @@ query_planner(PlannerInfo *root, List *tlist,
 	root->right_join_clauses = NIL;
 	root->full_join_clauses = NIL;
 	root->join_info_list = NIL;
+	root->lateral_info_list = NIL;
 	root->placeholder_list = NIL;
 	root->initial_rels = NIL;
 
@@ -178,9 +179,17 @@ query_planner(PlannerInfo *root, List *tlist,
 
 	find_placeholders_in_jointree(root);
 
+	find_lateral_references(root);
+
 	joinlist = deconstruct_jointree(root);
 
 	/*
+	 * Create the LateralJoinInfo list now that we have finalized
+	 * PlaceHolderVar eval levels.
+	 */
+	create_lateral_join_info(root);
+
+	/*
 	 * Reconsider any postponed outer-join quals now that we have built up
 	 * equivalence classes.  (This could result in further additions or
 	 * mergings of classes.)