Now that plans have flat rangetable lists, it's a lot easier to get EXPLAIN to

drill down into subplan targetlists to print the referent expression for an
OUTER or INNER var in an upper plan node.  Hence, make it do that always, and
banish the old hack of showing "?columnN?" when things got too complicated.

Along the way, fix an EXPLAIN bug I introduced by suppressing subqueries from
execution-time range tables: get_name_for_var_field() assumed it could look at
rte->subquery to find out the real type of a RECORD var.  That doesn't work
anymore, but instead we can look at the input plan of the SubqueryScan plan
node.

src/backend/optimizer/plan/setrefs.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/setrefs.c,v 1.132 2007/02/22 23:44:25 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/setrefs.c,v 1.133 2007/02/23 21:59:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -73,6 +73,7 @@ static void set_join_references(Join *join, int rtoffset);
 static void set_inner_join_references(Plan *inner_plan,
 						  indexed_tlist *outer_itlist);
 static void set_upper_references(Plan *plan, int rtoffset);
+static void set_dummy_tlist_references(Plan *plan, int rtoffset);
 static indexed_tlist *build_tlist_index(List *tlist);
 static Var *search_indexed_tlist_for_var(Var *var,
 							 indexed_tlist *itlist,
@@ -315,8 +316,7 @@ set_plan_refs(PlannerGlobal *glob, Plan *plan, int rtoffset)
 			 * executor, we fix it up for possible use by EXPLAIN (not to
 			 * mention ease of debugging --- wrong varnos are very confusing).
 			 */
-			plan->targetlist =
-				fix_scan_list(plan->targetlist, rtoffset);
+			set_dummy_tlist_references(plan, rtoffset);
 			/*
 			 * Since these plan types don't check quals either, we should not
 			 * find any qual expression attached to them.
@@ -330,11 +330,12 @@ set_plan_refs(PlannerGlobal *glob, Plan *plan, int rtoffset)
 				/*
 				 * Like the plan types above, Limit doesn't evaluate its tlist
 				 * or quals.  It does have live expressions for limit/offset,
-				 * however.
+				 * however; and those cannot contain subplan variable refs,
+				 * so fix_scan_expr works for them.
 				 */
-				splan->plan.targetlist =
-					fix_scan_list(splan->plan.targetlist, rtoffset);
+				set_dummy_tlist_references(plan, rtoffset);
 				Assert(splan->plan.qual == NIL);
+
 				splan->limitOffset =
 					fix_scan_expr(splan->limitOffset, rtoffset);
 				splan->limitCount =
@@ -375,8 +376,7 @@ set_plan_refs(PlannerGlobal *glob, Plan *plan, int rtoffset)
 				 * Append, like Sort et al, doesn't actually evaluate its
 				 * targetlist or check quals.
 				 */
-				splan->plan.targetlist =
-					fix_scan_list(splan->plan.targetlist, rtoffset);
+				set_dummy_tlist_references(plan, rtoffset);
 				Assert(splan->plan.qual == NIL);
 				foreach(l, splan->appendplans)
 				{
@@ -892,10 +892,7 @@ set_upper_references(Plan *plan, int rtoffset)
 	List	   *output_targetlist;
 	ListCell   *l;
 
-	if (subplan != NULL)
-		subplan_itlist = build_tlist_index(subplan->targetlist);
-	else
-		subplan_itlist = build_tlist_index(NIL);
+	subplan_itlist = build_tlist_index(subplan->targetlist);
 
 	output_targetlist = NIL;
 	foreach(l, plan->targetlist)
@@ -920,6 +917,58 @@ set_upper_references(Plan *plan, int rtoffset)
 	pfree(subplan_itlist);
 }
 
+/*
+ * set_dummy_tlist_references
+ *	  Replace the targetlist of an upper-level plan node with a simple
+ *	  list of OUTER references to its child.
+ *
+ * This is used for plan types like Sort and Append that don't evaluate
+ * their targetlists.  Although the executor doesn't care at all what's in
+ * the tlist, EXPLAIN needs it to be realistic.
+ *
+ * Note: we could almost use set_upper_references() here, but it fails for
+ * Append for lack of a lefttree subplan.  Single-purpose code is faster
+ * anyway.
+ */
+static void
+set_dummy_tlist_references(Plan *plan, int rtoffset)
+{
+	List	   *output_targetlist;
+	ListCell   *l;
+
+	output_targetlist = NIL;
+	foreach(l, plan->targetlist)
+	{
+		TargetEntry *tle = (TargetEntry *) lfirst(l);
+		Var		   *oldvar = (Var *) tle->expr;
+		Var		   *newvar;
+
+		newvar = makeVar(OUTER,
+						 tle->resno,
+						 exprType((Node *) oldvar),
+						 exprTypmod((Node *) oldvar),
+						 0);
+		if (IsA(oldvar, Var))
+		{
+			newvar->varnoold = oldvar->varno + rtoffset;
+			newvar->varoattno = oldvar->varattno;
+		}
+		else
+		{
+			newvar->varnoold = 0;	/* wasn't ever a plain Var */
+			newvar->varoattno = 0;
+		}
+
+		tle = flatCopyTargetEntry(tle);
+		tle->expr = (Expr *) newvar;
+		output_targetlist = lappend(output_targetlist, tle);
+	}
+	plan->targetlist = output_targetlist;
+
+	/* We don't touch plan->qual here */
+}
+
+
 /*
  * build_tlist_index --- build an index data structure for a child tlist
  *

src/include/utils/builtins.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/builtins.h,v 1.288 2007/02/17 00:55:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/utils/builtins.h,v 1.289 2007/02/23 21:59:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -537,10 +537,8 @@ extern Datum pg_get_serial_sequence(PG_FUNCTION_ARGS);
 extern char *deparse_expression(Node *expr, List *dpcontext,
 				   bool forceprefix, bool showimplicit);
 extern List *deparse_context_for(const char *aliasname, Oid relid);
-extern List *deparse_context_for_plan(int outer_varno, Node *outercontext,
-						 int inner_varno, Node *innercontext,
-						 List *rtable);
-extern Node *deparse_context_for_subplan(const char *name, Node *subplan);
+extern List *deparse_context_for_plan(Node *outer_plan, Node *inner_plan,
+									  List *rtable);
 extern const char *quote_identifier(const char *ident);
 extern char *quote_qualified_identifier(const char *namespace,
 						   const char *ident);