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Department of second thoughts: fix newly-added code in planner.c to make real 

sure that DISTINCT ON does what it's supposed to, ie, sort by the full ORDER
BY list before unique-ifying.  The error seems masked in simple cases by the
fact that query_planner won't return query pathkeys that only partially match
the requested sort order, but I wouldn't want to bet that it couldn't be
exposed in some way or other.
This commit is contained in:
Tom Lane 2008-08-05 16:03:10 +00:00
parent 2965400275
commit c78248c91d
1 changed files with 30 additions and 8 deletions
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38
src/backend/optimizer/plan/planner.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.238 2008/08/05 02:43:17 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.239 2008/08/05 16:03:10 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1304,11 +1304,24 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
/*
* Use a Unique node to implement DISTINCT. Add an explicit sort
* if we couldn't make the path come out the way the Unique node
* needs it. If we do have to sort, sort by the more rigorous
* of DISTINCT and ORDER BY, to avoid a second sort below.
* needs it. If we do have to sort, always sort by the more
* rigorous of DISTINCT and ORDER BY, to avoid a second sort
* below. However, for regular DISTINCT, don't sort now if we
* don't have to --- sorting afterwards will likely be cheaper,
* and also has the possibility of optimizing via LIMIT. But
* for DISTINCT ON, we *must* force the final sort now, else
* it won't have the desired behavior.
*/
if (!pathkeys_contained_in(root->distinct_pathkeys,
current_pathkeys))
List *needed_pathkeys;
if (parse->hasDistinctOn &&
list_length(root->distinct_pathkeys) <
list_length(root->sort_pathkeys))
needed_pathkeys = root->sort_pathkeys;
else
needed_pathkeys = root->distinct_pathkeys;
if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
{
if (list_length(root->distinct_pathkeys) >=
list_length(root->sort_pathkeys))
@ -1961,6 +1974,7 @@ choose_hashed_distinct(PlannerInfo *root,
int numDistinctCols = list_length(root->parse->distinctClause);
Size hashentrysize;
List *current_pathkeys;
List *needed_pathkeys;
Path hashed_p;
Path sorted_p;
@ -2002,13 +2016,21 @@ choose_hashed_distinct(PlannerInfo *root,
cost_sort(&hashed_p, root, root->sort_pathkeys, hashed_p.total_cost,
dNumDistinctRows, input_plan->plan_width, limit_tuples);
/* Now for the GROUP case ... */
/*
* Now for the GROUP case. See comments in grouping_planner about the
* sorting choices here --- this code should match that code.
*/
sorted_p.startup_cost = input_plan->startup_cost;
sorted_p.total_cost = input_plan->total_cost;
current_pathkeys = input_pathkeys;
if (!pathkeys_contained_in(root->distinct_pathkeys, current_pathkeys))
if (root->parse->hasDistinctOn &&
list_length(root->distinct_pathkeys) <
list_length(root->sort_pathkeys))
needed_pathkeys = root->sort_pathkeys;
else
needed_pathkeys = root->distinct_pathkeys;
if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
{
/* We don't want to sort twice */
if (list_length(root->distinct_pathkeys) >=
list_length(root->sort_pathkeys))
current_pathkeys = root->distinct_pathkeys;