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Postgres FD Implementation
Commit 421467cd authored by Tom Lane's avatar Tom Lane
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Fix optimizer to not try to push WHERE clauses down into a sub-SELECT that 

has a DISTINCT ON clause, per bug report from Anthony Wood.  While at it,
improve the DISTINCT-ON-clause recognizer routine to not be fooled by out-
of-order DISTINCT lists.
parent 6fbf442d
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Showing with 70 additions and 40 deletions
src/backend/optimizer/path/allpaths.c
View file @ 421467cd
......@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.77 2001/07/16 17:57:02 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.78 2001/07/31 17:56:30 tgl Exp $
*
*-------------------------------------------------------------------------
*/
......@@ -296,8 +296,12 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
* the quals down into the component queries of the setop, but getting it
* right seems nontrivial. Work on this later.)
*
* 2. If the subquery has a LIMIT clause we must not push down any quals,
* since that could change the set of rows returned.
* 2. If the subquery has a LIMIT clause or a DISTINCT ON clause, we must
* not push down any quals, since that could change the set of rows
* returned. (Actually, we could push down quals into a DISTINCT ON
* subquery if they refer only to DISTINCT-ed output columns, but checking
* that seems more work than it's worth. In any case, a plain DISTINCT is
* safe to push down past.)
*
* 3. We do not push down clauses that contain subselects, mainly because
* I'm not sure it will work correctly (the subplan hasn't yet transformed
......@@ -311,7 +315,8 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
*/
if (subquery->setOperations == NULL &&
subquery->limitOffset == NULL &&
subquery->limitCount == NULL)
subquery->limitCount == NULL &&
!has_distinct_on_clause(subquery))
{
/* OK to consider pushing down individual quals */
List *upperrestrictlist = NIL;
......
src/backend/optimizer/util/clauses.c
View file @ 421467cd
......@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.86 2001/06/19 22:39:11 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.87 2001/07/31 17:56:31 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
......@@ -728,6 +728,58 @@ pull_constant_clauses(List *quals, List **constantQual)
}
/*****************************************************************************
* Tests on clauses of queries
*
* Possibly this code should go someplace else, since this isn't quite the
* same meaning of "clause" as is used elsewhere in this module. But I can't
* think of a better place for it...
*****************************************************************************/
/*
* Test whether a query uses DISTINCT ON, ie, has a distinct-list that is
* just a subset of the output columns.
*/
bool
has_distinct_on_clause(Query *query)
{
List *targetList;
/* Is there a DISTINCT clause at all? */
if (query->distinctClause == NIL)
return false;
/*
* If the DISTINCT list contains all the nonjunk targetlist items,
* then it's a simple DISTINCT, else it's DISTINCT ON. We do not
* require the lists to be in the same order (since the parser may
* have adjusted the DISTINCT clause ordering to agree with ORDER BY).
*/
foreach(targetList, query->targetList)
{
TargetEntry *tle = (TargetEntry *) lfirst(targetList);
Index ressortgroupref;
List *distinctClause;
if (tle->resdom->resjunk)
continue;
ressortgroupref = tle->resdom->ressortgroupref;
if (ressortgroupref == 0)
return true; /* definitely not in DISTINCT list */
foreach(distinctClause, query->distinctClause)
{
SortClause *scl = (SortClause *) lfirst(distinctClause);
if (scl->tleSortGroupRef == ressortgroupref)
break; /* found TLE in DISTINCT */
}
if (distinctClause == NIL)
return true; /* this TLE is not in DISTINCT list */
}
/* It's a simple DISTINCT */
return false;
}
/*****************************************************************************
* *
* General clause-manipulating routines *
......@@ -735,7 +787,7 @@ pull_constant_clauses(List *quals, List **constantQual)
*****************************************************************************/
/*
* clause_relids_vars
* clause_get_relids_vars
* Retrieves distinct relids and vars appearing within a clause.
*
* '*relids' is set to an integer list of all distinct "varno"s appearing
......
src/backend/utils/adt/ruleutils.c
View file @ 421467cd
......@@ -3,7 +3,7 @@
* back to source text
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/adt/ruleutils.c,v 1.80 2001/07/16 05:06:59 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/adt/ruleutils.c,v 1.81 2001/07/31 17:56:31 tgl Exp $
*
* This software is copyrighted by Jan Wieck - Hamburg.
*
......@@ -119,7 +119,6 @@ static void get_utility_query_def(Query *query, deparse_context *context);
static void get_basic_select_query(Query *query, deparse_context *context);
static void get_setop_query(Node *setOp, Query *query,
deparse_context *context, bool toplevel);
static bool simple_distinct(List *distinctClause, List *targetList);
static void get_rule_sortgroupclause(SortClause *srt, List *tlist,
bool force_colno,
deparse_context *context);
......@@ -1064,9 +1063,7 @@ get_basic_select_query(Query *query, deparse_context *context)
/* Add the DISTINCT clause if given */
if (query->distinctClause != NIL)
{
if (simple_distinct(query->distinctClause, query->targetList))
appendStringInfo(buf, " DISTINCT");
else
if (has_distinct_on_clause(query))
{
appendStringInfo(buf, " DISTINCT ON (");
sep = "";
......@@ -1081,6 +1078,8 @@ get_basic_select_query(Query *query, deparse_context *context)
}
appendStringInfo(buf, ")");
}
else
appendStringInfo(buf, " DISTINCT");
}
/* Then we tell what to select (the targetlist) */
......@@ -1207,34 +1206,6 @@ get_setop_query(Node *setOp, Query *query, deparse_context *context,
}
}
/*
* Detect whether a DISTINCT list can be represented as just DISTINCT
* or needs DISTINCT ON. It's simple if it contains exactly the nonjunk
* targetlist items.
*/
static bool
simple_distinct(List *distinctClause, List *targetList)
{
while (targetList)
{
TargetEntry *tle = (TargetEntry *) lfirst(targetList);
if (!tle->resdom->resjunk)
{
if (distinctClause == NIL)
return false;
if (((SortClause *) lfirst(distinctClause))->tleSortGroupRef !=
tle->resdom->ressortgroupref)
return false;
distinctClause = lnext(distinctClause);
}
targetList = lnext(targetList);
}
if (distinctClause != NIL)
return false;
return true;
}
/*
* Display a sort/group clause.
*/
......
src/include/optimizer/clauses.h
View file @ 421467cd
......@@ -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 1.44 2001/05/20 20:28:20 tgl Exp $
* $Id: clauses.h,v 1.45 2001/07/31 17:56:31 tgl Exp $
*
*-------------------------------------------------------------------------
*/
......@@ -51,6 +51,8 @@ extern bool contain_noncachable_functions(Node *clause);
extern bool is_pseudo_constant_clause(Node *clause);
extern List *pull_constant_clauses(List *quals, List **constantQual);
extern bool has_distinct_on_clause(Query *query);
extern void clause_get_relids_vars(Node *clause, Relids *relids, List **vars);
extern int NumRelids(Node *clause);
extern void CommuteClause(Expr *clause);
......
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