Implement SQL-standard LATERAL subqueries.

This patch implements the standard syntax of LATERAL attached to a
sub-SELECT in FROM, and also allows LATERAL attached to a function in FROM,
since set-returning function calls are expected to be one of the principal
use-cases.

The main change here is a rewrite of the mechanism for keeping track of
which relations are visible for column references while the FROM clause is
being scanned.  The parser "namespace" lists are no longer lists of bare
RTEs, but are lists of ParseNamespaceItem structs, which carry an RTE
pointer as well as some visibility-controlling flags.  Aside from
supporting LATERAL correctly, this lets us get rid of the ancient hacks
that required rechecking subqueries and JOIN/ON and function-in-FROM
expressions for invalid references after they were initially parsed.
Invalid column references are now always correctly detected on sight.

In passing, remove assorted parser error checks that are now dead code by
virtue of our having gotten rid of add_missing_from, as well as some
comments that are obsolete for the same reason.  (It was mainly
add_missing_from that caused so much fudging here in the first place.)

The planner support for this feature is very minimal, and will be improved
in future patches.  It works well enough for testing purposes, though.

catversion bump forced due to new field in RangeTblEntry.

1 files changed, 26 insertions, 4 deletions

diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 65f86194e15..fe0e4d7c201 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -491,12 +491,18 @@ sort_inner_and_outer(PlannerInfo *root,
 	 * explosion of mergejoin paths of dubious value.  This interacts with
 	 * decisions elsewhere that also discriminate against mergejoins with
 	 * parameterized inputs; see comments in src/backend/optimizer/README.
-	 *
-	 * If unique-ification is requested, do it and then handle as a plain
-	 * inner join.
 	 */
 	outer_path = outerrel->cheapest_total_path;
 	inner_path = innerrel->cheapest_total_path;
+
+	/* Punt if either rel has only parameterized paths */
+	if (!outer_path || !inner_path)
+		return;
+
+	/*
+	 * If unique-ification is requested, do it and then handle as a plain
+	 * inner join.
+	 */
 	if (jointype == JOIN_UNIQUE_OUTER)
 	{
 		outer_path = (Path *) create_unique_path(root, outerrel,
@@ -696,6 +702,10 @@ match_unsorted_outer(PlannerInfo *root,
 	 */
 	if (save_jointype == JOIN_UNIQUE_INNER)
 	{
+		/* XXX for the moment, don't crash on LATERAL --- rethink this */
+		if (inner_cheapest_total == NULL)
+			return;
+
 		inner_cheapest_total = (Path *)
 			create_unique_path(root, innerrel, inner_cheapest_total, sjinfo);
 		Assert(inner_cheapest_total);
@@ -707,7 +717,7 @@ match_unsorted_outer(PlannerInfo *root,
 		 * enable_material is off or the path in question materializes its
 		 * output anyway.
 		 */
-		if (enable_material &&
+		if (enable_material && inner_cheapest_total != NULL &&
 			!ExecMaterializesOutput(inner_cheapest_total->pathtype))
 			matpath = (Path *)
 				create_material_path(innerrel, inner_cheapest_total);
@@ -735,6 +745,8 @@ match_unsorted_outer(PlannerInfo *root,
 		 * If we need to unique-ify the outer path, it's pointless to consider
 		 * any but the cheapest outer.	(XXX we don't consider parameterized
 		 * outers, nor inners, for unique-ified cases.	Should we?)
+		 *
+		 * XXX does nothing for LATERAL, rethink
 		 */
 		if (save_jointype == JOIN_UNIQUE_OUTER)
 		{
@@ -814,6 +826,10 @@ match_unsorted_outer(PlannerInfo *root,
 		if (save_jointype == JOIN_UNIQUE_OUTER)
 			continue;
 
+		/* Can't do anything else if inner has no unparameterized paths */
+		if (!inner_cheapest_total)
+			continue;
+
 		/* Look for useful mergeclauses (if any) */
 		mergeclauses = find_mergeclauses_for_pathkeys(root,
 													  outerpath->pathkeys,
@@ -1092,6 +1108,12 @@ hash_inner_and_outer(PlannerInfo *root,
 		Path	   *cheapest_total_outer = outerrel->cheapest_total_path;
 		Path	   *cheapest_total_inner = innerrel->cheapest_total_path;
 
+		/* Punt if either rel has only parameterized paths */
+		if (!cheapest_startup_outer ||
+			!cheapest_total_outer ||
+			!cheapest_total_inner)
+			return;
+
 		/* Unique-ify if need be; we ignore parameterized possibilities */
 		if (jointype == JOIN_UNIQUE_OUTER)
 		{