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Commitfcba3b8

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Tweak trivial_subqueryscan() to consider a SubqueryScan's targetlist
trivial if it contains either Vars referencing the corresponding subplancolumns, or Consts equaling the corresponding subplan columns. Thislets the planner eliminate the SubqueryScan in some cases generated bygenerate_setop_tlist().
1 parent88b8110 commitfcba3b8

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‎src/backend/optimizer/plan/setrefs.c

Lines changed: 24 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@
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*
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*
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* IDENTIFICATION
12-
* $PostgreSQL: pgsql/src/backend/optimizer/plan/setrefs.c,v 1.124 2006/08/12 02:52:05 tgl Exp $
12+
* $PostgreSQL: pgsql/src/backend/optimizer/plan/setrefs.c,v 1.125 2006/08/28 14:32:41 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -448,16 +448,32 @@ trivial_subqueryscan(SubqueryScan *plan)
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{
449449
TargetEntry*ptle= (TargetEntry*)lfirst(lp);
450450
TargetEntry*ctle= (TargetEntry*)lfirst(lc);
451-
Var*var= (Var*)ptle->expr;
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453452
if (ptle->resjunk!=ctle->resjunk)
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return false;/* tlist doesn't match junk status */
455-
if (!var|| !IsA(var,Var))
456-
return false;/* tlist item not a Var */
457-
Assert(var->varno==plan->scan.scanrelid);
458-
Assert(var->varlevelsup==0);
459-
if (var->varattno!=attrno)
460-
return false;/* out of order */
454+
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/*
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* We accept either a Var referencing the corresponding element of
457+
* the subplan tlist, or a Const equaling the subplan element.
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* See generate_setop_tlist() for motivation.
459+
*/
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if (ptle->expr&&IsA(ptle->expr,Var))
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{
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Var*var= (Var*)ptle->expr;
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Assert(var->varno==plan->scan.scanrelid);
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Assert(var->varlevelsup==0);
466+
if (var->varattno!=attrno)
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return false;/* out of order */
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}
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elseif (ptle->expr&&IsA(ptle->expr,Const))
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{
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if (!equal(ptle->expr,ctle->expr))
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return false;
473+
}
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else
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return false;
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461477
attrno++;
462478
}
463479

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