Restructure planning code so that preprocessing of targetlist and quals

to simplify constant expressions and expand SubLink nodes into SubPlans
is done in a separate routine subquery_planner() that calls union_planner().
We formerly did most of this work in query_planner(), but that's the
wrong place because it may never see the real targetlist.  Splitting
union_planner into two routines also allows us to avoid redundant work
when union_planner is invoked recursively for UNION and inheritance
cases.  Upshot is that it is now possible to do something like
select float8(count(*)) / (select count(*) from int4_tbl)  from int4_tbl
group by f1;
which has never worked before.

src/backend/optimizer/README

@@ -132,14 +132,14 @@ than applying a sort to the cheapest other path).
 Optimizer Functions
 -------------------
 
+The primary entry point is planner().
+
 planner()
- handle inheritance by processing separately
+ set up for recursive handling of subqueries
--init_query_planner()
+ do final cleanup after planning.
-  preprocess target list
+-subquery_planner()
-  preprocess qualifications(WHERE)
+ simplify constant expressions
---query_planner()
+ canonicalize qual
-   simplify constant subexpressions
-   canonicalize_qual()
      Attempt to reduce WHERE clause to either CNF or DNF canonical form.
      CNF (top-level-AND) is preferred, since the optimizer can then use
      any of the AND subclauses to filter tuples; but quals that are in
@@ -147,6 +147,13 @@ planner()
      force them to CNF.  In pathological cases either transform may expand
      the qual unreasonably; so we may have to leave it un-normalized,
      thereby reducing the accuracy of selectivity estimates.
+ process sublinks
+ convert Vars of outer query levels into Params
+--union_planner()
+  handle unions and inheritance by mutual recursion with prepunion.c routines
+  preprocess target list
+  handle GROUP BY, HAVING, aggregates, ORDER BY, DISTINCT
+--query_planner()
    pull out constants from target list
    get a target list that only contains column names, no expressions
    if none, then return

src/backend/optimizer/plan/planmain.c

@@ -3,29 +3,31 @@
  * planmain.c
  *	  Routines to plan a single query
  *
+ * What's in a name, anyway?  The top-level entry point of the planner/
+ * optimizer is over in planner.c, not here as you might think from the
+ * file name.  But this is the main code for planning a basic join operation,
+ * shorn of features like subselects, inheritance, aggregates, grouping,
+ * and so on.  (Those are the things planner.c deals with.)
+ *
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planmain.c,v 1.52 2000/02/15 20:49:18 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planmain.c,v 1.53 2000/03/21 05:11:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
-#include <sys/types.h>
-
 #include "postgres.h"
 
+#include <sys/types.h>
 
 #include "optimizer/clauses.h"
 #include "optimizer/cost.h"
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
 #include "optimizer/planmain.h"
-#include "optimizer/prep.h"
-#include "optimizer/subselect.h"
 #include "optimizer/tlist.h"
-#include "utils/lsyscache.h"
 
 
 static Plan *subplanner(Query *root, List *flat_tlist, List *qual,
@@ -34,19 +36,15 @@ static Plan *subplanner(Query *root, List *flat_tlist, List *qual,
 
 /*--------------------
  * query_planner
- *	  Routine to create a query plan.  It does so by first creating a
+ *	  Generate a plan for a basic query, which may involve joins but
- *	  subplan for the topmost level of attributes in the query.  Then,
+ *	  not any fancier features.
- *	  it modifies all target list and qualifications to consider the next
- *	  level of nesting and creates a plan for this modified query by
- *	  recursively calling itself.  The two pieces are then merged together
- *	  by creating a result node that indicates which attributes should
- *	  be placed where and any relation level qualifications to be
- *	  satisfied.
  *
- * tlist is the target list of the query (do NOT use root->targetList!)
+ * tlist is the target list the query should produce (NOT root->targetList!)
  * qual is the qualification of the query (likewise!)
  * tuple_fraction is the fraction of tuples we expect will be retrieved
  *
+ * qual must already have been converted to implicit-AND form.
+ *
  * Note: the Query node now also includes a query_pathkeys field, which
  * is both an input and an output of query_planner().  The input value
  * signals query_planner that the indicated sort order is wanted in the
@@ -83,46 +81,6 @@ query_planner(Query *root,
 	List	   *var_only_tlist;
 	Plan	   *subplan;
 
-	/*
-	 * Note: union_planner should already have done constant folding
-	 * in both the tlist and qual, so we don't do it again here
-	 * (indeed, we may be getting a flattened var-only tlist anyway).
-	 *
-	 * Is there any value in re-folding the qual after canonicalize_qual?
-	 */
-
-	/*
-	 * Canonicalize the qual, and convert it to implicit-AND format.
-	 */
-	qual = canonicalize_qual((Expr *) qual, true);
-#ifdef OPTIMIZER_DEBUG
-	printf("After canonicalize_qual()\n");
-	pprint(qual);
-#endif
-
-	/* Replace uplevel vars with Param nodes */
-	if (PlannerQueryLevel > 1)
-	{
-		tlist = (List *) SS_replace_correlation_vars((Node *) tlist);
-		qual = (List *) SS_replace_correlation_vars((Node *) qual);
-	}
-
-	/* Expand SubLinks to SubPlans */
-	if (root->hasSubLinks)
-	{
-		tlist = (List *) SS_process_sublinks((Node *) tlist);
-		qual = (List *) SS_process_sublinks((Node *) qual);
-		if (root->groupClause != NIL)
-		{
-			/*
-			 * Check for ungrouped variables passed to subplans.
-			 * Note we do NOT do this for subplans in WHERE; it's legal
-			 * there because WHERE is evaluated pre-GROUP.
-			 */
-			check_subplans_for_ungrouped_vars((Node *) tlist, root, tlist);
-		}
-	}
-
 	/*
 	 * If the query contains no relation references at all, it must be
 	 * something like "SELECT 2+2;".  Build a trivial "Result" plan.
@@ -192,16 +150,6 @@ query_planner(Query *root,
 	}
 
 	return subplan;
-
-#ifdef NOT_USED
-
-	/*
-	 * Destructively modify the query plan's targetlist to add fjoin lists
-	 * to flatten functions that return sets of base types
-	 */
-	subplan->targetlist = generate_fjoin(subplan->targetlist);
-#endif
-
 }
 
 /*

src/backend/optimizer/plan/planner.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.77 2000/03/14 02:23:15 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.78 2000/03/21 05:12:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -36,6 +36,7 @@
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
 
+
 static List *make_subplanTargetList(Query *parse, List *tlist,
 									AttrNumber **groupColIdx);
 static Plan *make_groupplan(List *group_tlist, bool tuplePerGroup,
@@ -59,23 +60,154 @@ planner(Query *parse)
 	PlannerParamVar = NULL;
 	PlannerPlanId = 0;
 
+	/* this should go away sometime soon */
 	transformKeySetQuery(parse);
 
-	result_plan = union_planner(parse, -1.0 /* default case */);
+	/* primary planning entry point (may recurse for subplans) */
+	result_plan = subquery_planner(parse, -1.0 /* default case */);
 
 	Assert(PlannerQueryLevel == 1);
+
+	/* if top-level query had subqueries, do housekeeping for them */
 	if (PlannerPlanId > 0)
 	{
-		result_plan->initPlan = PlannerInitPlan;
 		(void) SS_finalize_plan(result_plan);
+		result_plan->initPlan = PlannerInitPlan;
 	}
+
+	/* executor wants to know total number of Params used overall */
 	result_plan->nParamExec = length(PlannerParamVar);
 
+	/* final cleanup of the plan */
 	set_plan_references(result_plan);
 
 	return result_plan;
 }
 
+
+/*--------------------
+ * subquery_planner
+ *	  Invokes the planner on a subquery.  We recurse to here for each
+ *	  sub-SELECT found in the query tree.
+ *
+ * parse is the querytree produced by the parser & rewriter.
+ * tuple_fraction is the fraction of tuples we expect will be retrieved.
+ * tuple_fraction is interpreted as explained for union_planner, below.
+ *
+ * Basically, this routine does the stuff that should only be done once
+ * per Query object.  It then calls union_planner, which may be called
+ * recursively on the same Query node in order to handle UNIONs and/or
+ * inheritance.  subquery_planner is called recursively from subselect.c.
+ *
+ * prepunion.c uses an unholy combination of calling union_planner when
+ * recursing on the primary Query node, or subquery_planner when recursing
+ * on a UNION'd Query node that hasn't previously been seen by
+ * subquery_planner.  That whole chunk of code needs rewritten from scratch.
+ *
+ * Returns a query plan.
+ *--------------------
+ */
+Plan *
+subquery_planner(Query *parse, double tuple_fraction)
+{
+	/*
+	 * A HAVING clause without aggregates is equivalent to a WHERE clause
+	 * (except it can only refer to grouped fields).  If there are no
+	 * aggs anywhere in the query, then we don't want to create an Agg
+	 * plan node, so merge the HAVING condition into WHERE.  (We used to
+	 * consider this an error condition, but it seems to be legal SQL.)
+	 */
+	if (parse->havingQual != NULL && ! parse->hasAggs)
+	{
+		if (parse->qual == NULL)
+			parse->qual = parse->havingQual;
+		else
+			parse->qual = (Node *) make_andclause(lappend(lcons(parse->qual,
+																NIL),
+														  parse->havingQual));
+		parse->havingQual = NULL;
+	}
+
+	/*
+	 * Simplify constant expressions in targetlist and quals.
+	 *
+	 * Note that at this point the qual has not yet been converted to
+	 * implicit-AND form, so we can apply eval_const_expressions directly.
+	 * Also note that we need to do this before SS_process_sublinks,
+	 * because that routine inserts bogus "Const" nodes.
+	 */
+	parse->targetList = (List *)
+		eval_const_expressions((Node *) parse->targetList);
+	parse->qual = eval_const_expressions(parse->qual);
+	parse->havingQual = eval_const_expressions(parse->havingQual);
+
+	/*
+	 * Canonicalize the qual, and convert it to implicit-AND format.
+	 *
+	 * XXX Is there any value in re-applying eval_const_expressions
+	 * after canonicalize_qual?
+	 */
+	parse->qual = (Node *) canonicalize_qual((Expr *) parse->qual, true);
+#ifdef OPTIMIZER_DEBUG
+	printf("After canonicalize_qual()\n");
+	pprint(parse->qual);
+#endif
+
+	/*
+	 * Ditto for the havingQual
+	 */
+	parse->havingQual = (Node *) canonicalize_qual((Expr *) parse->havingQual,
+												   true);
+
+	/* Expand SubLinks to SubPlans */
+	if (parse->hasSubLinks)
+	{
+		parse->targetList = (List *)
+			SS_process_sublinks((Node *) parse->targetList);
+		parse->qual = SS_process_sublinks(parse->qual);
+		parse->havingQual = SS_process_sublinks(parse->havingQual);
+
+		if (parse->groupClause != NIL)
+		{
+			/*
+			 * Check for ungrouped variables passed to subplans.
+			 * Note we do NOT do this for subplans in WHERE; it's legal
+			 * there because WHERE is evaluated pre-GROUP.
+			 *
+			 * An interesting fine point: if we reassigned a HAVING qual
+			 * into WHERE above, then we will accept references to ungrouped
+			 * vars from subplans in the HAVING qual.  This is not entirely
+			 * consistent, but it doesn't seem particularly harmful...
+			 */
+			check_subplans_for_ungrouped_vars((Node *) parse->targetList,
+											  parse);
+			check_subplans_for_ungrouped_vars(parse->havingQual, parse);
+		}
+	}
+
+	/* Replace uplevel vars with Param nodes */
+	if (PlannerQueryLevel > 1)
+	{
+		parse->targetList = (List *)
+			SS_replace_correlation_vars((Node *) parse->targetList);
+		parse->qual = SS_replace_correlation_vars(parse->qual);
+		parse->havingQual = SS_replace_correlation_vars(parse->havingQual);
+	}
+
+	/* Do the main planning (potentially recursive) */
+
+	return union_planner(parse, tuple_fraction);
+
+	/*
+	 * XXX should any more of union_planner's activity be moved here?
+	 *
+	 * That would take careful study of the interactions with prepunion.c,
+	 * but I suspect it would pay off in simplicity and avoidance of
+	 * wasted cycles.
+	 */
+}
+
+
 /*--------------------
  * union_planner
  *	  Invokes the planner on union-type queries (both regular UNIONs and
@@ -111,37 +243,6 @@ union_planner(Query *parse,
 	List	   *sort_pathkeys;
 	Index		rt_index;
 
-	/*
-	 * A HAVING clause without aggregates is equivalent to a WHERE clause
-	 * (except it can only refer to grouped fields).  If there are no
-	 * aggs anywhere in the query, then we don't want to create an Agg
-	 * plan node, so merge the HAVING condition into WHERE.  (We used to
-	 * consider this an error condition, but it seems to be legal SQL.)
-	 */
-	if (parse->havingQual != NULL && ! parse->hasAggs)
-	{
-		if (parse->qual == NULL)
-			parse->qual = parse->havingQual;
-		else
-			parse->qual = (Node *) make_andclause(lappend(lcons(parse->qual,
-																NIL),
-														  parse->havingQual));
-		parse->havingQual = NULL;
-	}
-
-	/*
-	 * Simplify constant expressions in targetlist and quals.
-	 *
-	 * Note that at this point the qual has not yet been converted to
-	 * implicit-AND form, so we can apply eval_const_expressions directly.
-	 * Also note that we need to do this before SS_process_sublinks,
-	 * because that routine inserts bogus "Const" nodes.
-	 */
-	tlist = (List *) eval_const_expressions((Node *) tlist);
-	parse->qual = eval_const_expressions(parse->qual);
-	parse->havingQual = eval_const_expressions(parse->havingQual);
-
-
 	if (parse->unionClause)
 	{
 		result_plan = (Plan *) plan_union_queries(parse);
@@ -474,32 +575,6 @@ union_planner(Query *parse,
 									 result_plan);
 	}
 
-	/*
-	 * If we have a HAVING clause, do the necessary things with it.
-	 * This code should parallel query_planner()'s initial processing
-	 * of the WHERE clause.
-	 */
-	if (parse->havingQual)
-	{
-		/* Convert the havingQual to implicit-AND normal form */
-		parse->havingQual = (Node *)
-			canonicalize_qual((Expr *) parse->havingQual, true);
-
-		/* Replace uplevel Vars with Params */
-		if (PlannerQueryLevel > 1)
-			parse->havingQual = SS_replace_correlation_vars(parse->havingQual);
-
-		if (parse->hasSubLinks)
-		{
-			/* Expand SubLinks to SubPlans */
-			parse->havingQual = SS_process_sublinks(parse->havingQual);
-			/* Check for ungrouped variables passed to subplans */
-			check_subplans_for_ungrouped_vars(parse->havingQual,
-											  parse,
-											  parse->targetList);
-		}
-	}
-
 	/*
 	 * If aggregate is present, insert the Agg node
 	 *

src/backend/optimizer/plan/subselect.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.32 2000/03/17 02:36:15 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.33 2000/03/21 05:12:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -163,7 +163,7 @@ make_subplan(SubLink *slink)
 	else
 		tuple_fraction = -1.0;	/* default behavior */
 
-	node->plan = plan = union_planner(subquery, tuple_fraction);
+	node->plan = plan = subquery_planner(subquery, tuple_fraction);
 
 	/*
 	 * Assign subPlan, extParam and locParam to plan nodes. At the moment,

src/backend/optimizer/prep/prepunion.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.46 2000/03/14 23:06:29 thomas Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.47 2000/03/21 05:12:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -149,8 +149,12 @@ plan_union_queries(Query *parse)
 		{
 			Query	   *union_query = lfirst(ulist);
 
+			/* use subquery_planner here because the union'd queries
+			 * have not been preprocessed yet.  My goodness this is messy...
+			 */
 			union_plans = lappend(union_plans,
-								  union_planner(union_query, tuple_fraction));
+								  subquery_planner(union_query,
+												   tuple_fraction));
 			union_rts = lappend(union_rts, union_query->rtable);
 		}
 	}
@@ -185,8 +189,11 @@ plan_union_queries(Query *parse)
 		{
 			Query	   *union_all_query = lfirst(ulist);
 
+			/* use subquery_planner here because the union'd queries
+			 * have not been preprocessed yet.  My goodness this is messy...
+			 */
 			union_plans = lappend(union_plans,
-								  union_planner(union_all_query, -1.0));
+								  subquery_planner(union_all_query, -1.0));
 			union_rts = lappend(union_rts, union_all_query->rtable);
 		}
 	}

src/backend/optimizer/util/clauses.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.62 2000/03/19 18:20:38 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.63 2000/03/21 05:12:12 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -41,15 +41,10 @@
 	((Node *) makeConst(BOOLOID, 1, (Datum) (val), \
 						(isnull), true, false, false))
 
-typedef struct {
-	Query	   *query;
-	List	   *targetList;
-} check_subplans_for_ungrouped_vars_context;
-
 static bool contain_agg_clause_walker(Node *node, void *context);
 static bool pull_agg_clause_walker(Node *node, List **listptr);
 static bool check_subplans_for_ungrouped_vars_walker(Node *node,
-					check_subplans_for_ungrouped_vars_context *context);
+													 Query *context);
 static int is_single_func(Node *node);
 static Node *eval_const_expressions_mutator (Node *node, void *context);
 static Expr *simplify_op_or_func(Expr *expr, List *args);
@@ -467,30 +462,24 @@ pull_agg_clause_walker(Node *node, List **listptr)
  * In most contexts, ungrouped variables will be detected by the parser (see
  * parse_agg.c, check_ungrouped_columns()). But that routine currently does
  * not check subplans, because the necessary info is not computed until the
- * planner runs.  So we do it here, after we have processed the subplan.
+ * planner runs.  So we do it here, after we have processed sublinks into
- * This ought to be cleaned up someday.
+ * subplans.  This ought to be cleaned up someday.
  *
  * 'clause' is the expression tree to be searched for subplans.
- * 'query' provides the GROUP BY list and range table.
+ * 'query' provides the GROUP BY list, the target list that the group clauses
- * 'targetList' is the target list that the group clauses refer to.
+ * refer to, and the range table.
- * (Is it really necessary to pass the tlist separately?  Couldn't we
- * just use the tlist found in the query node?)
  */
 void
 check_subplans_for_ungrouped_vars(Node *clause,
-								  Query *query,
+								  Query *query)
-								  List *targetList)
 {
-	check_subplans_for_ungrouped_vars_context context;
+	/* No special setup needed; context for walker is just the Query pointer */
-
+	check_subplans_for_ungrouped_vars_walker(clause, query);
-	context.query = query;
-	context.targetList = targetList;
-	check_subplans_for_ungrouped_vars_walker(clause, &context);
 }
 
 static bool
 check_subplans_for_ungrouped_vars_walker(Node *node,
-					check_subplans_for_ungrouped_vars_context *context)
+										 Query *context)
 {
 	if (node == NULL)
 		return false;
@@ -529,7 +518,7 @@ check_subplans_for_ungrouped_vars_walker(Node *node,
 			 * Else, see if it is a grouping column.
 			 */
 			contained_in_group_clause = false;
-			foreach(gl, context->query->groupClause)
+			foreach(gl, context->groupClause)
 			{
 				GroupClause	   *gcl = lfirst(gl);
 				Node		   *groupexpr;
@@ -550,8 +539,8 @@ check_subplans_for_ungrouped_vars_walker(Node *node,
 				char		   *attname;
 
 				Assert(var->varno > 0 &&
-					   var->varno <= length(context->query->rtable));
+					   var->varno <= length(context->rtable));
-				rte = rt_fetch(var->varno, context->query->rtable);
+				rte = rt_fetch(var->varno, context->rtable);
 				attname = get_attname(rte->relid, var->varattno);
 				if (! attname)
 					elog(ERROR, "cache lookup of attribute %d in relation %u failed",

src/include/optimizer/clauses.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: clauses.h,v 1.33 2000/01/26 05:58:20 momjian Exp $
+ * $Id: clauses.h,v 1.34 2000/03/21 05:11:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,9 +41,7 @@ extern List *make_ands_implicit(Expr *clause);
 extern List *pull_constant_clauses(List *quals, List **constantQual);
 extern bool contain_agg_clause(Node *clause);
 extern List *pull_agg_clause(Node *clause);
-extern void check_subplans_for_ungrouped_vars(Node *clause,
+extern void check_subplans_for_ungrouped_vars(Node *clause, Query *query);
-											  Query *query,
-											  List *targetList);
 
 extern void clause_get_relids_vars(Node *clause, Relids *relids, List **vars);
 extern int	NumRelids(Node *clause);

src/include/optimizer/planner.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: planner.h,v 1.14 2000/02/15 20:49:26 tgl Exp $
+ * $Id: planner.h,v 1.15 2000/03/21 05:11:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,6 +21,7 @@
 #include "nodes/plannodes.h"
 
 extern Plan *planner(Query *parse);
+extern Plan *subquery_planner(Query *parse, double tuple_fraction);
 extern Plan *union_planner(Query *parse, double tuple_fraction);
 extern void pg_checkretval(Oid rettype, List *querytree_list);