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Commitc5e59bb

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Teach reparameterize_path() to handle AppendPaths.
If we're inside a lateral subquery, there may be no unparameterized pathsfor a particular child relation of an appendrel, in which case we *must*be able to create similarly-parameterized paths for each other childrelation, else the planner will fail with "could not devise a query planfor the given query". This means that there are situations where we'dbetter be able to reparameterize at least one path for each child.This calls into question the assumption in reparameterize_path() thatit can just punt if it feels like it. However, the only case that isknown broken right now is where the child is itself an appendrel so thatall its paths are AppendPaths. (I think possibly I disregarded that inthe original coding on the theory that nested appendrels would get foldedtogether --- but that only happens *after* reparameterize_path(), so it'snot excused from handling a child AppendPath.) Given that this code's beenlike this since 9.3 when LATERAL was introduced, it seems likely we'd haveheard of other cases by now if there were a larger problem.Per report from Elvis Pranskevichus. Back-patch to 9.3.Discussion:https://postgr.es/m/5981018.zdth1YWmNy@hammer.magicstack.net
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3 files changed

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‎src/backend/optimizer/util/pathnode.c

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3423,6 +3423,30 @@ reparameterize_path(PlannerInfo *root, Path *path,
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spath->path.pathkeys,
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required_outer);
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}
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caseT_Append:
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{
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AppendPath*apath= (AppendPath*)path;
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List*childpaths=NIL;
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ListCell*lc;
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/* Reparameterize the children */
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foreach(lc,apath->subpaths)
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{
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Path*spath= (Path*)lfirst(lc);
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spath=reparameterize_path(root,spath,
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required_outer,
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loop_count);
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if (spath==NULL)
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returnNULL;
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childpaths=lappend(childpaths,spath);
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}
3444+
return (Path*)
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create_append_path(rel,childpaths,
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required_outer,
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apath->path.parallel_workers,
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apath->partitioned_rels);
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}
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default:
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break;
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}

‎src/test/regress/expected/join.out

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Original file line numberDiff line numberDiff line change
@@ -5154,6 +5154,25 @@ select * from
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Output: 3
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(11 rows)
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-- check handling of nested appendrels inside LATERAL
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select * from
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((select 2 as v) union all (select 3 as v)) as q1
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cross join lateral
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((select * from
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((select 4 as v) union all (select 5 as v)) as q3)
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union all
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(select q1.v)
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) as q2;
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v | v
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---+---
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2 | 4
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2 | 5
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2 | 2
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3 | 4
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3 | 5
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3 | 3
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(6 rows)
5175+
51575176
-- check we don't try to do a unique-ified semijoin with LATERAL
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explain (verbose, costs off)
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select * from

‎src/test/regress/sql/join.sql

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1668,6 +1668,16 @@ select * from
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select*from (select3as z offset0) zwherez.z=x.x
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) zzonzz.z=y.y;
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-- check handling of nested appendrels inside LATERAL
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select*from
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((select2as v)union all (select3as v))as q1
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cross join lateral
1675+
((select*from
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((select4as v)union all (select5as v))as q3)
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union all
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(selectq1.v)
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)as q2;
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-- check we don't try to do a unique-ified semijoin with LATERAL
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explain (verbose, costs off)
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select*from

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