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Fix some issues with improper placement of outer join clauses.

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After applying outer-join identity 3 in the forward direction,
it was possible for the planner to mistakenly apply a qual clause
from above the two outer joins at the now-lower join level.
This can give the wrong answer, since a value that would get nulled
by the now-upper join might not yet be null.

To fix, when we perform such a transformation, consider that the
now-lower join hasn't really completed the outer join it's nominally
responsible for and thus its relid set should not include that OJ's
relid (nor should its output Vars have that nullingrel bit set).
Instead we add those bits when the now-upper join is performed.
The existing rules for qual placement then suffice to prevent
higher qual clauses from dropping below the now-upper join.
There are a few complications from needing to consider transitive
closures in case multiple pushdowns have happened, but all in all
it's not a very complex patch.

This is all new logic (from 2489d76c4) so no need to back-patch.
The added test cases all have the same results as in v15.

Tom Lane and Richard Guo

Discussion: https://postgr.es/m/0b819232-4b50-f245-1c7d-c8c61bf41827@postgrespro.ru
This commit is contained in:
Tom Lane
2023-05-17 11:13:52 -04:00
parent 867be9c073
commit 9df8f903eb
14 changed files with 449 additions and 85 deletions
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58
src/backend/optimizer/plan/initsplan.c
View File

@ -1213,8 +1213,8 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem)
* positioning decisions will be made later, when we revisit the
* postponed clauses.
*/
if (sjinfo->commute_below)
ojscope = bms_add_members(ojscope, sjinfo->commute_below);
ojscope = bms_add_members(ojscope, sjinfo->commute_below_l);
ojscope = bms_add_members(ojscope, sjinfo->commute_below_r);
}
else
postponed_oj_qual_list = NULL;
@ -1400,7 +1400,8 @@ make_outerjoininfo(PlannerInfo *root,
/* these fields may get added to later: */
sjinfo->commute_above_l = NULL;
sjinfo->commute_above_r = NULL;
sjinfo->commute_below = NULL;
sjinfo->commute_below_l = NULL;
sjinfo->commute_below_r = NULL;
compute_semijoin_info(root, sjinfo, clause);
@ -1643,37 +1644,30 @@ make_outerjoininfo(PlannerInfo *root,
* Now that we've identified the correct min_lefthand and min_righthand,
* any commute_below_l or commute_below_r relids that have not gotten
* added back into those sets (due to intervening outer joins) are indeed
* commutable with this one. Update the derived data in the
* SpecialJoinInfos.
* commutable with this one.
*
* First, delete any subsequently-added-back relids (this is easier than
* maintaining commute_below_l/r precisely through all the above).
*/
commute_below_l = bms_del_members(commute_below_l, min_lefthand);
commute_below_r = bms_del_members(commute_below_r, min_righthand);
/* Anything left? */
if (commute_below_l || commute_below_r)
{
Relids commute_below;
/*
* Delete any subsequently-added-back relids (this is easier than
* maintaining commute_below_l/r precisely through all the above).
*/
commute_below_l = bms_del_members(commute_below_l, min_lefthand);
commute_below_r = bms_del_members(commute_below_r, min_righthand);
/* Anything left? */
commute_below = bms_union(commute_below_l, commute_below_r);
if (!bms_is_empty(commute_below))
/* Yup, so we must update the derived data in the SpecialJoinInfos */
sjinfo->commute_below_l = commute_below_l;
sjinfo->commute_below_r = commute_below_r;
foreach(l, root->join_info_list)
{
/* Yup, so we must update the data structures */
sjinfo->commute_below = commute_below;
foreach(l, root->join_info_list)
{
SpecialJoinInfo *otherinfo = (SpecialJoinInfo *) lfirst(l);
SpecialJoinInfo *otherinfo = (SpecialJoinInfo *) lfirst(l);
if (bms_is_member(otherinfo->ojrelid, commute_below_l))
otherinfo->commute_above_l =
bms_add_member(otherinfo->commute_above_l, ojrelid);
else if (bms_is_member(otherinfo->ojrelid, commute_below_r))
otherinfo->commute_above_r =
bms_add_member(otherinfo->commute_above_r, ojrelid);
}
if (bms_is_member(otherinfo->ojrelid, commute_below_l))
otherinfo->commute_above_l =
bms_add_member(otherinfo->commute_above_l, ojrelid);
else if (bms_is_member(otherinfo->ojrelid, commute_below_r))
otherinfo->commute_above_r =
bms_add_member(otherinfo->commute_above_r, ojrelid);
}
}
@ -1889,8 +1883,7 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
* as-is.
*/
Assert(sjinfo->lhs_strict); /* else we shouldn't be here */
if (sjinfo->commute_above_r ||
bms_overlap(sjinfo->commute_below, sjinfo->syn_lefthand))
if (sjinfo->commute_above_r || sjinfo->commute_below_l)
{
Relids joins_above;
Relids joins_below;
@ -1901,8 +1894,7 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
/* Identify the outer joins this one commutes with */
joins_above = sjinfo->commute_above_r;
joins_below = bms_intersect(sjinfo->commute_below,
sjinfo->syn_lefthand);
joins_below = sjinfo->commute_below_l;
/*
* Generate qual variants with different sets of nullingrels bits.