From 96ca8ffebcb43df1c575ce6831324c553a31c891 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 30 Oct 2001 19:58:58 +0000
Subject: [PATCH] Fix problems with subselects used in GROUP BY expressions,
per gripe from Philip Warner. Side effect of change is that GROUP BY
expressions will not be re-evaluated at multiple plan levels anymore, whereas
this sometimes happened with old code.
---
src/backend/optimizer/plan/planner.c | 40 ++++----
src/backend/optimizer/plan/setrefs.c | 137 +++++++++++++++------------
src/backend/optimizer/util/clauses.c | 89 ++++++++++++-----
src/include/optimizer/clauses.h | 4 +-
4 files changed, 167 insertions(+), 103 deletions(-)
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index d13035ca9ca..faca5728e6b 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.111 2001/10/28 06:25:45 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.112 2001/10/30 19:58:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -173,6 +173,17 @@ subquery_planner(Query *parse, double tuple_fraction)
parse->havingQual = preprocess_expression(parse, parse->havingQual,
EXPRKIND_HAVING);
+ /*
+ * Check for ungrouped variables passed to subplans in targetlist and
+ * HAVING clause (but not in WHERE or JOIN/ON clauses, since those are
+ * evaluated before grouping). We can't do this any earlier because
+ * we must use the preprocessed targetlist for comparisons of grouped
+ * expressions.
+ */
+ if (parse->hasSubLinks &&
+ (parse->groupClause != NIL || parse->hasAggs))
+ check_subplans_for_ungrouped_vars(parse);
+
/*
* A HAVING clause without aggregates is equivalent to a WHERE clause
* (except it can only refer to grouped fields). Transfer any
@@ -623,23 +634,10 @@ preprocess_expression(Query *parse, Node *expr, int kind)
#endif
}
+ /* Expand SubLinks to SubPlans */
if (parse->hasSubLinks)
- {
- /* Expand SubLinks to SubPlans */
expr = SS_process_sublinks(expr);
- if (kind != EXPRKIND_WHERE &&
- (parse->groupClause != NIL || parse->hasAggs))
- {
- /*
- * Check for ungrouped variables passed to subplans. Note we
- * do NOT do this for subplans in WHERE (or JOIN/ON); it's
- * legal there because WHERE is evaluated pre-GROUP.
- */
- check_subplans_for_ungrouped_vars(expr, parse);
- }
- }
-
/* Replace uplevel vars with Param nodes */
if (PlannerQueryLevel > 1)
expr = SS_replace_correlation_vars(expr);
@@ -1122,12 +1120,11 @@ grouping_planner(Query *parse, double tuple_fraction)
/*
* If there are aggregates then the Group node should just return
- * the same set of vars as the subplan did (but we can exclude any
- * GROUP BY expressions). If there are no aggregates then the
- * Group node had better compute the final tlist.
+ * the same set of vars as the subplan did. If there are no aggs
+ * then the Group node had better compute the final tlist.
*/
if (parse->hasAggs)
- group_tlist = flatten_tlist(result_plan->targetlist);
+ group_tlist = new_unsorted_tlist(result_plan->targetlist);
else
group_tlist = tlist;
@@ -1234,7 +1231,10 @@ grouping_planner(Query *parse, double tuple_fraction)
* where the a+b target will be used by the Sort/Group steps, and the
* other targets will be used for computing the final results. (In the
* above example we could theoretically suppress the a and b targets and
- * use only a+b, but it's not really worth the trouble.)
+ * pass down only c,d,a+b, but it's not really worth the trouble to
+ * eliminate simple var references from the subplan. We will avoid doing
+ * the extra computation to recompute a+b at the outer level; see
+ * replace_vars_with_subplan_refs() in setrefs.c.)
*
* 'parse' is the query being processed.
* 'tlist' is the query's target list.
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index e7f8361b9a7..652e7c294a0 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.71 2001/03/22 03:59:37 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/setrefs.c,v 1.72 2001/10/30 19:58:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -33,7 +33,8 @@ typedef struct
typedef struct
{
Index subvarno;
- List *subplanTargetList;
+ List *subplan_targetlist;
+ bool tlist_has_non_vars;
} replace_vars_with_subplan_refs_context;
static void fix_expr_references(Plan *plan, Node *node);
@@ -43,7 +44,8 @@ static Node *join_references_mutator(Node *node,
join_references_context *context);
static Node *replace_vars_with_subplan_refs(Node *node,
Index subvarno,
- List *subplanTargetList);
+ List *subplan_targetlist,
+ bool tlist_has_non_vars);
static Node *replace_vars_with_subplan_refs_mutator(Node *node,
replace_vars_with_subplan_refs_context *context);
static bool fix_opids_walker(Node *node, void *context);
@@ -278,75 +280,62 @@ set_join_references(Join *join)
* qual expressions with elements of the subplan's tlist (which was
* generated by flatten_tlist() from these selfsame expressions, so it
* should have all the required variables). There is an important exception,
- * however: a GROUP BY expression that is also an output expression will
- * have been pushed into the subplan tlist unflattened. We want to detect
- * this case and reference the subplan output directly. Therefore, check
- * for equality of the whole tlist expression to any subplan element before
- * we resort to picking the expression apart for individual Vars.
+ * however: GROUP BY and ORDER BY expressions will have been pushed into the
+ * subplan tlist unflattened. If these values are also needed in the output
+ * then we want to reference the subplan tlist element rather than recomputing
+ * the expression.
*/
static void
set_uppernode_references(Plan *plan, Index subvarno)
{
Plan *subplan = plan->lefttree;
- List *subplanTargetList,
- *outputTargetList,
+ List *subplan_targetlist,
+ *output_targetlist,
*l;
+ bool tlist_has_non_vars;
if (subplan != NULL)
- subplanTargetList = subplan->targetlist;
+ subplan_targetlist = subplan->targetlist;
else
- subplanTargetList = NIL;
+ subplan_targetlist = NIL;
- outputTargetList = NIL;
- foreach(l, plan->targetlist)
+ /*
+ * Detect whether subplan tlist has any non-Vars (typically it won't
+ * because it's been flattened). This allows us to save comparisons
+ * in common cases.
+ */
+ tlist_has_non_vars = false;
+ foreach(l, subplan_targetlist)
{
TargetEntry *tle = (TargetEntry *) lfirst(l);
- TargetEntry *subplantle;
- Node *newexpr;
-
- subplantle = tlistentry_member(tle->expr, subplanTargetList);
- if (subplantle)
- {
- /* Found a matching subplan output expression */
- Resdom *resdom = subplantle->resdom;
- Var *newvar;
- newvar = makeVar(subvarno,
- resdom->resno,
- resdom->restype,
- resdom->restypmod,
- 0);
- /* If we're just copying a simple Var, copy up original info */
- if (subplantle->expr && IsA(subplantle->expr, Var))
- {
- Var *subvar = (Var *) subplantle->expr;
-
- newvar->varnoold = subvar->varnoold;
- newvar->varoattno = subvar->varoattno;
- }
- else
- {
- newvar->varnoold = 0;
- newvar->varoattno = 0;
- }
- newexpr = (Node *) newvar;
- }
- else
+ if (tle->expr && ! IsA(tle->expr, Var))
{
- /* No matching expression, so replace individual Vars */
- newexpr = replace_vars_with_subplan_refs(tle->expr,
- subvarno,
- subplanTargetList);
+ tlist_has_non_vars = true;
+ break;
}
- outputTargetList = lappend(outputTargetList,
- makeTargetEntry(tle->resdom, newexpr));
}
- plan->targetlist = outputTargetList;
+
+ output_targetlist = NIL;
+ foreach(l, plan->targetlist)
+ {
+ TargetEntry *tle = (TargetEntry *) lfirst(l);
+ Node *newexpr;
+
+ newexpr = replace_vars_with_subplan_refs(tle->expr,
+ subvarno,
+ subplan_targetlist,
+ tlist_has_non_vars);
+ output_targetlist = lappend(output_targetlist,
+ makeTargetEntry(tle->resdom, newexpr));
+ }
+ plan->targetlist = output_targetlist;
plan->qual = (List *)
replace_vars_with_subplan_refs((Node *) plan->qual,
subvarno,
- subplanTargetList);
+ subplan_targetlist,
+ tlist_has_non_vars);
}
/*
@@ -439,9 +428,16 @@ join_references_mutator(Node *node,
* --- so this routine should only be applied to nodes whose subplans'
* targetlists were generated via flatten_tlist() or some such method.
*
- * 'node': the tree to be fixed (a targetlist or qual list)
+ * If tlist_has_non_vars is true, then we try to match whole subexpressions
+ * against elements of the subplan tlist, so that we can avoid recomputing
+ * expressions that were already computed by the subplan. (This is relatively
+ * expensive, so we don't want to try it in the common case where the
+ * subplan tlist is just a flattened list of Vars.)
+ *
+ * 'node': the tree to be fixed (a target item or qual)
* 'subvarno': varno to be assigned to all Vars
- * 'subplanTargetList': target list for subplan
+ * 'subplan_targetlist': target list for subplan
+ * 'tlist_has_non_vars': true if subplan_targetlist contains non-Var exprs
*
* The resulting tree is a copy of the original in which all Var nodes have
* varno = subvarno, varattno = resno of corresponding subplan target.
@@ -450,12 +446,14 @@ join_references_mutator(Node *node,
static Node *
replace_vars_with_subplan_refs(Node *node,
Index subvarno,
- List *subplanTargetList)
+ List *subplan_targetlist,
+ bool tlist_has_non_vars)
{
replace_vars_with_subplan_refs_context context;
context.subvarno = subvarno;
- context.subplanTargetList = subplanTargetList;
+ context.subplan_targetlist = subplan_targetlist;
+ context.tlist_has_non_vars = tlist_has_non_vars;
return replace_vars_with_subplan_refs_mutator(node, &context);
}
@@ -468,17 +466,38 @@ replace_vars_with_subplan_refs_mutator(Node *node,
if (IsA(node, Var))
{
Var *var = (Var *) node;
- Var *newvar = (Var *) copyObject(var);
Resdom *resdom;
+ Var *newvar;
- resdom = tlist_member((Node *) var, context->subplanTargetList);
+ resdom = tlist_member((Node *) var, context->subplan_targetlist);
if (!resdom)
elog(ERROR, "replace_vars_with_subplan_refs: variable not in subplan target list");
-
+ newvar = (Var *) copyObject(var);
newvar->varno = context->subvarno;
newvar->varattno = resdom->resno;
return (Node *) newvar;
}
+ /* Try matching more complex expressions too, if tlist has any */
+ if (context->tlist_has_non_vars)
+ {
+ Resdom *resdom;
+
+ resdom = tlist_member(node, context->subplan_targetlist);
+ if (resdom)
+ {
+ /* Found a matching subplan output expression */
+ Var *newvar;
+
+ newvar = makeVar(context->subvarno,
+ resdom->resno,
+ resdom->restype,
+ resdom->restypmod,
+ 0);
+ newvar->varnoold = 0; /* wasn't ever a plain Var */
+ newvar->varoattno = 0;
+ return (Node *) newvar;
+ }
+ }
return expression_tree_mutator(node,
replace_vars_with_subplan_refs_mutator,
(void *) context);
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index c92581082b2..859c409709c 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.89 2001/10/25 05:49:34 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.90 2001/10/30 19:58:58 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@@ -39,12 +39,18 @@
((Node *) makeConst(BOOLOID, 1, (Datum) (val), \
(isnull), true, false, false))
+typedef struct
+{
+ Query *query;
+ List *groupClauses;
+} 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 contain_subplans_walker(Node *node, void *context);
static bool pull_subplans_walker(Node *node, List **listptr);
static bool check_subplans_for_ungrouped_vars_walker(Node *node,
- Query *context);
+ check_subplans_for_ungrouped_vars_context *context);
static bool contain_noncachable_functions_walker(Node *node, void *context);
static Node *eval_const_expressions_mutator(Node *node, void *context);
static Expr *simplify_op_or_func(Expr *expr, List *args);
@@ -517,36 +523,81 @@ pull_subplans_walker(Node *node, List **listptr)
* planner runs. So we do it here, after we have processed sublinks into
* subplans. This ought to be cleaned up someday.
*
- * 'clause' is the expression tree to be searched for subplans.
- * 'query' provides the GROUP BY list, the target list that the group clauses
- * refer to, and the range table.
+ * A deficiency in this scheme is that any outer reference var must be
+ * grouped by itself; we don't recognize groupable expressions within
+ * subselects. For example, consider
+ * SELECT
+ * (SELECT x FROM bar where y = (foo.a + foo.b))
+ * FROM foo
+ * GROUP BY a + b;
+ * This query will be rejected although it could be allowed.
*/
void
-check_subplans_for_ungrouped_vars(Node *clause,
- Query *query)
+check_subplans_for_ungrouped_vars(Query *query)
{
+ check_subplans_for_ungrouped_vars_context context;
+ List *gl;
+
+ context.query = query;
+ /*
+ * Build a list of the acceptable GROUP BY expressions for use in
+ * the walker (to avoid repeated scans of the targetlist within the
+ * recursive routine).
+ */
+ context.groupClauses = NIL;
+ foreach(gl, query->groupClause)
+ {
+ GroupClause *grpcl = lfirst(gl);
+ Node *expr;
+
+ expr = get_sortgroupclause_expr(grpcl, query->targetList);
+ context.groupClauses = lcons(expr, context.groupClauses);
+ }
+
/*
- * No special setup needed; context for walker is just the Query
- * pointer
+ * Recursively scan the targetlist and the HAVING clause.
+ * WHERE and JOIN/ON conditions are not examined, since they are
+ * evaluated before grouping.
*/
- check_subplans_for_ungrouped_vars_walker(clause, query);
+ check_subplans_for_ungrouped_vars_walker((Node *) query->targetList,
+ &context);
+ check_subplans_for_ungrouped_vars_walker(query->havingQual,
+ &context);
+
+ freeList(context.groupClauses);
}
static bool
check_subplans_for_ungrouped_vars_walker(Node *node,
- Query *context)
+ check_subplans_for_ungrouped_vars_context *context)
{
+ List *gl;
+
if (node == NULL)
return false;
+ if (IsA(node, Const) || IsA(node, Param))
+ return false; /* constants are always acceptable */
/*
* If we find an aggregate function, do not recurse into its
* arguments. Subplans invoked within aggregate calls are allowed to
- * receive ungrouped variables.
+ * receive ungrouped variables. (This test and the next one should
+ * match the logic in parse_agg.c's check_ungrouped_columns().)
*/
if (IsA(node, Aggref))
return false;
+ /*
+ * Check to see if subexpression as a whole matches any GROUP BY item.
+ * We need to do this at every recursion level so that we recognize
+ * GROUPed-BY expressions before reaching variables within them.
+ */
+ foreach(gl, context->groupClauses)
+ {
+ if (equal(node, lfirst(gl)))
+ return false; /* acceptable, do not descend more */
+ }
+
/*
* We can ignore Vars other than in subplan args lists, since the
* parser already checked 'em.
@@ -564,7 +615,6 @@ check_subplans_for_ungrouped_vars_walker(Node *node,
Node *thisarg = lfirst(t);
Var *var;
bool contained_in_group_clause;
- List *gl;
/*
* We do not care about args that are not local variables;
@@ -582,14 +632,9 @@ check_subplans_for_ungrouped_vars_walker(Node *node,
* Else, see if it is a grouping column.
*/
contained_in_group_clause = false;
- foreach(gl, context->groupClause)
+ foreach(gl, context->groupClauses)
{
- GroupClause *gcl = lfirst(gl);
- Node *groupexpr;
-
- groupexpr = get_sortgroupclause_expr(gcl,
- context->targetList);
- if (equal(thisarg, groupexpr))
+ if (equal(thisarg, lfirst(gl)))
{
contained_in_group_clause = true;
break;
@@ -603,8 +648,8 @@ check_subplans_for_ungrouped_vars_walker(Node *node,
char *attname;
Assert(var->varno > 0 &&
- (int) var->varno <= length(context->rtable));
- rte = rt_fetch(var->varno, context->rtable);
+ (int) var->varno <= length(context->query->rtable));
+ rte = rt_fetch(var->varno, context->query->rtable);
attname = get_rte_attribute_name(rte, var->varattno);
elog(ERROR, "Sub-SELECT uses un-GROUPed attribute %s.%s from outer query",
rte->eref->relname, attname);
diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h
index aa97bcc862c..da8429ca094 100644
--- a/src/include/optimizer/clauses.h
+++ b/src/include/optimizer/clauses.h
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: clauses.h,v 1.47 2001/10/28 06:26:07 momjian Exp $
+ * $Id: clauses.h,v 1.48 2001/10/30 19:58:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -44,7 +44,7 @@ extern List *pull_agg_clause(Node *clause);
extern bool contain_subplans(Node *clause);
extern List *pull_subplans(Node *clause);
-extern void check_subplans_for_ungrouped_vars(Node *clause, Query *query);
+extern void check_subplans_for_ungrouped_vars(Query *query);
extern bool contain_noncachable_functions(Node *clause);
--
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