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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2010-09-28 12:08:56 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2010-09-28 14:19:00 -0400 |
| commit | eb229505103eb5494c33832d422584bfdee03fc6 (patch) | |
| tree | ca7c12732d170cb5abef8f108b2d95f508444b7c /src/backend/optimizer/plan/planmain.c | |
| parent | 9c5f4f6cb50dd22028acc0b6f20291a5edcac62b (diff) | |
Fix PlaceHolderVar mechanism's interaction with outer joins.
The point of a PlaceHolderVar is to allow a non-strict expression to be
evaluated below an outer join, after which its value bubbles up like a Var
and can be forced to NULL when the outer join's semantics require that.
However, there was a serious design oversight in that, namely that we
didn't ensure that there was actually a correct place in the plan tree
to evaluate the placeholder :-(. It may be necessary to delay evaluation
of an outer join to ensure that a placeholder that should be evaluated
below the join can be evaluated there. Per recent bug report from Kirill
Simonov.
Back-patch to 8.4 where the PlaceHolderVar mechanism was introduced.
Diffstat (limited to 'src/backend/optimizer/plan/planmain.c')
| -rw-r--r-- | src/backend/optimizer/plan/planmain.c | 23 |
1 files changed, 15 insertions, 8 deletions
diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c index e82c3404b53..9e884cbb3cb 100644 --- a/src/backend/optimizer/plan/planmain.c +++ b/src/backend/optimizer/plan/planmain.c @@ -180,14 +180,19 @@ query_planner(PlannerInfo *root, List *tlist, add_base_rels_to_query(root, (Node *) parse->jointree); /* - * Examine the targetlist and qualifications, adding entries to baserel - * targetlists for all referenced Vars. Restrict and join clauses are - * added to appropriate lists belonging to the mentioned relations. We - * also build EquivalenceClasses for provably equivalent expressions, and - * form a target joinlist for make_one_rel() to work from. + * Examine the targetlist and join tree, adding entries to baserel + * targetlists for all referenced Vars, and generating PlaceHolderInfo + * entries for all referenced PlaceHolderVars. Restrict and join clauses + * are added to appropriate lists belonging to the mentioned relations. + * We also build EquivalenceClasses for provably equivalent expressions. + * The SpecialJoinInfo list is also built to hold information about join + * order restrictions. Finally, we form a target joinlist for + * make_one_rel() to work from. */ build_base_rel_tlists(root, tlist); + find_placeholders_in_jointree(root); + joinlist = deconstruct_jointree(root); /* @@ -218,10 +223,12 @@ query_planner(PlannerInfo *root, List *tlist, /* * Examine any "placeholder" expressions generated during subquery pullup. - * Make sure that we know what level to evaluate them at, and that the - * Vars they need are marked as needed. + * Make sure that the Vars they need are marked as needed at the relevant + * join level. This must be done before join removal because it might + * cause Vars or placeholders to be needed above a join when they weren't + * so marked before. */ - fix_placeholder_eval_levels(root); + fix_placeholder_input_needed_levels(root); /* * Remove any useless outer joins. Ideally this would be done during |