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Major revision of sort-node handling: push knowledge of query

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sort order down into planner, instead of handling it only at the very top
level of the planner.  This fixes many things.  An explicit sort is now
avoided if there is a cheaper alternative (typically an indexscan) not
only for ORDER BY, but also for the internal sort of GROUP BY.  It works
even when there is no other reason (such as a WHERE condition) to consider
the indexscan.  It works for indexes on functions.  It works for indexes
on functions, backwards.  It's just so cool...

CAUTION: I have changed the representation of SortClause nodes, therefore
THIS UPDATE BREAKS STORED RULES.  You will need to initdb.
This commit is contained in:
Tom Lane
1999-08-21 03:49:17 +00:00
parent 5588c559e6
commit db436adf76
33 changed files with 967 additions and 1002 deletions
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15
src/backend/optimizer/prep/prepunion.c
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@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.38 1999/08/16 02:17:55 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.39 1999/08/21 03:49:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -159,7 +159,7 @@ plan_union_queries(Query *parse)
union_plans = lcons(union_planner(parse), NIL);
union_rts = lcons(parse->rtable, NIL);
/* Append the remainging UNION ALLs */
/* Append the remaining UNION ALLs */
foreach(ulist, union_all_queries)
{
Query *union_all_query = lfirst(ulist);
@@ -172,14 +172,19 @@ plan_union_queries(Query *parse)
/* We have already split UNION and UNION ALL and we made it consistent */
if (!last_union_all_flag)
{
/* Need SELECT DISTINCT behavior to implement UNION.
* Set uniqueFlag properly, put back the held sortClause,
* and add any missing columns to the sort clause.
*/
parse->uniqueFlag = "*";
parse->sortClause = transformSortClause(NULL, NIL,
hold_sortClause,
parse->targetList, "*");
parse->sortClause = addAllTargetsToSortList(hold_sortClause,
parse->targetList);
}
else
{
/* needed so we don't take the flag from the first query */
parse->uniqueFlag = NULL;
}
/* Make sure we don't try to apply the first query's grouping stuff
* to the Append node, either. Basically we don't want union_planner