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, 71 insertions, 13 deletions

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index f02954982a7..bfda05394d6 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -253,8 +253,9 @@ set_rel_size(PlannerInfo *root, RelOptInfo *rel,
 			case RTE_SUBQUERY:
 
 				/*
-				 * Subqueries don't support parameterized paths, so just go
-				 * ahead and build their paths immediately.
+				 * Subqueries don't support making a choice between
+				 * parameterized and unparameterized paths, so just go ahead
+				 * and build their paths immediately.
 				 */
 				set_subquery_pathlist(root, rel, rti, rte);
 				break;
@@ -698,6 +699,10 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 		if (IS_DUMMY_REL(childrel))
 			continue;
 
+		/* XXX need to figure out what to do for LATERAL */
+		if (childrel->cheapest_total_path == NULL)
+			elog(ERROR, "LATERAL within an append relation is not supported yet");
+
 		/*
 		 * Child is live, so add its cheapest access path to the Append path
 		 * we are constructing for the parent.
@@ -906,6 +911,10 @@ generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
 			 */
 			if (cheapest_startup == NULL || cheapest_total == NULL)
 			{
+				/* XXX need to figure out what to do for LATERAL */
+				if (childrel->cheapest_total_path == NULL)
+					elog(ERROR, "LATERAL within an append relation is not supported yet");
+
 				cheapest_startup = cheapest_total =
 					childrel->cheapest_total_path;
 				Assert(cheapest_total != NULL);
@@ -1012,8 +1021,13 @@ has_multiple_baserels(PlannerInfo *root)
  * set_subquery_pathlist
  *		Build the (single) access path for a subquery RTE
  *
- * There's no need for a separate set_subquery_size phase, since we don't
- * support parameterized paths for subqueries.
+ * We don't currently support generating parameterized paths for subqueries
+ * by pushing join clauses down into them; it seems too expensive to re-plan
+ * the subquery multiple times to consider different alternatives.	So the
+ * subquery will have exactly one path.  (The path will be parameterized
+ * if the subquery contains LATERAL references, otherwise not.)  Since there's
+ * no freedom of action here, there's no need for a separate set_subquery_size
+ * phase: we just make the path right away.
  */
 static void
 set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
@@ -1021,6 +1035,7 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 {
 	Query	   *parse = root->parse;
 	Query	   *subquery = rte->subquery;
+	Relids		required_outer;
 	bool	   *differentTypes;
 	double		tuple_fraction;
 	PlannerInfo *subroot;
@@ -1033,6 +1048,20 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 	 */
 	subquery = copyObject(subquery);
 
+	/*
+	 * If it's a LATERAL subquery, it might contain some Vars of the current
+	 * query level, requiring it to be treated as parameterized.
+	 */
+	if (rte->lateral)
+	{
+		required_outer = pull_varnos_of_level((Node *) subquery, 1);
+		/* Enforce convention that empty required_outer is exactly NULL */
+		if (bms_is_empty(required_outer))
+			required_outer = NULL;
+	}
+	else
+		required_outer = NULL;
+
 	/* We need a workspace for keeping track of set-op type coercions */
 	differentTypes = (bool *)
 		palloc0((list_length(subquery->targetList) + 1) * sizeof(bool));
@@ -1051,10 +1080,9 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 	 * pseudoconstant clauses; better to have the gating node above the
 	 * subquery.
 	 *
-	 * Also, if the sub-query has "security_barrier" flag, it means the
+	 * Also, if the sub-query has the "security_barrier" flag, it means the
 	 * sub-query originated from a view that must enforce row-level security.
-	 * We must not push down quals in order to avoid information leaks, either
-	 * via side-effects or error output.
+	 * Then we must not push down quals that contain leaky functions.
 	 *
 	 * Non-pushed-down clauses will get evaluated as qpquals of the
 	 * SubqueryScan node.
@@ -1134,7 +1162,7 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 	pathkeys = convert_subquery_pathkeys(root, rel, subroot->query_pathkeys);
 
 	/* Generate appropriate path */
-	add_path(rel, create_subqueryscan_path(root, rel, pathkeys, NULL));
+	add_path(rel, create_subqueryscan_path(root, rel, pathkeys, required_outer));
 
 	/* Select cheapest path (pretty easy in this case...) */
 	set_cheapest(rel);
@@ -1143,12 +1171,32 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 /*
  * set_function_pathlist
  *		Build the (single) access path for a function RTE
+ *
+ * As with subqueries, a function RTE's path might be parameterized due to
+ * LATERAL references, but that's inherent in the function expression and
+ * not a result of pushing down join quals.
  */
 static void
 set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 {
+	Relids		required_outer;
+
+	/*
+	 * If it's a LATERAL function, it might contain some Vars of the current
+	 * query level, requiring it to be treated as parameterized.
+	 */
+	if (rte->lateral)
+	{
+		required_outer = pull_varnos_of_level(rte->funcexpr, 0);
+		/* Enforce convention that empty required_outer is exactly NULL */
+		if (bms_is_empty(required_outer))
+			required_outer = NULL;
+	}
+	else
+		required_outer = NULL;
+
 	/* Generate appropriate path */
-	add_path(rel, create_functionscan_path(root, rel));
+	add_path(rel, create_functionscan_path(root, rel, required_outer));
 
 	/* Select cheapest path (pretty easy in this case...) */
 	set_cheapest(rel);
@@ -1157,6 +1205,10 @@ set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 /*
  * set_values_pathlist
  *		Build the (single) access path for a VALUES RTE
+ *
+ * There can be no need for a parameterized path here.	(Although the SQL
+ * spec does allow LATERAL (VALUES (x)), the parser will transform that
+ * into a subquery, so it doesn't end up here.)
  */
 static void
 set_values_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
@@ -1988,10 +2040,16 @@ debug_print_rel(PlannerInfo *root, RelOptInfo *rel)
 	printf("\tpath list:\n");
 	foreach(l, rel->pathlist)
 		print_path(root, lfirst(l), 1);
-	printf("\n\tcheapest startup path:\n");
-	print_path(root, rel->cheapest_startup_path, 1);
-	printf("\n\tcheapest total path:\n");
-	print_path(root, rel->cheapest_total_path, 1);
+	if (rel->cheapest_startup_path)
+	{
+		printf("\n\tcheapest startup path:\n");
+		print_path(root, rel->cheapest_startup_path, 1);
+	}
+	if (rel->cheapest_total_path)
+	{
+		printf("\n\tcheapest total path:\n");
+		print_path(root, rel->cheapest_total_path, 1);
+	}
 	printf("\n");
 	fflush(stdout);
 }