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Commita43f430

Browse files
committed
Improve has_nullable_targetlist() to allow strict functions of simple
variables, not just simple variables. This was foreseen in the originalcoding of this routine, but not implemented until now. Responds toperformance gripe from Laurent Perez.
1 parent47f8f33 commita43f430

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2 files changed

+36
-28
lines changed

2 files changed

+36
-28
lines changed

‎src/backend/optimizer/prep/prepjointree.c

Lines changed: 15 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -16,7 +16,7 @@
1616
*
1717
*
1818
* IDENTIFICATION
19-
* $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.15 2004/01/1000:30:21 tgl Exp $
19+
* $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.16 2004/01/1018:13:53 tgl Exp $
2020
*
2121
*-------------------------------------------------------------------------
2222
*/
@@ -439,11 +439,13 @@ is_simple_subquery(Query *subquery)
439439
/*
440440
* has_nullable_targetlist
441441
* Check a subquery in the range table to see if all the non-junk
442-
* targetlist items are simple variables (and, hence, will correctly
443-
* go to NULL when examined above the point of an outer join).
442+
* targetlist items are simple variables or strict functions of simple
443+
* variables (and, hence, will correctly go to NULL when examined above
444+
* the point of an outer join).
444445
*
445-
* A possible future extension is to accept strict functions of simple
446-
* variables, eg, "x + 1".
446+
* NOTE: it would be correct (and useful) to ignore output columns that aren't
447+
* actually referenced by the enclosing query ... but we do not have that
448+
* information available at this point.
447449
*/
448450
staticbool
449451
has_nullable_targetlist(Query*subquery)
@@ -458,11 +460,15 @@ has_nullable_targetlist(Query *subquery)
458460
if (tle->resdom->resjunk)
459461
continue;
460462

461-
/*Okay if tlist item is a simple Var */
462-
if (tle->expr&&IsA(tle->expr,Var))
463-
continue;
463+
/*Must contain a Var of current level */
464+
if (!contain_vars_of_level((Node*)tle->expr,0))
465+
return false;
464466

465-
return false;
467+
/* Must not contain any non-strict constructs */
468+
if (contain_nonstrict_functions((Node*)tle->expr))
469+
return false;
470+
471+
/* This one's OK, keep scanning */
466472
}
467473
return true;
468474
}

‎src/backend/optimizer/util/clauses.c

Lines changed: 21 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.160 2004/01/05 18:04:39 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.161 2004/01/10 18:13:53 tgl Exp $
1212
*
1313
* HISTORY
1414
* AUTHORDATEMAJOR EVENT
@@ -697,10 +697,10 @@ contain_volatile_functions_walker(Node *node, void *context)
697697
* Returns true if any nonstrict construct is found --- ie, anything that
698698
* could produce non-NULL output with a NULL input.
699699
*
700-
*XXX we do not examine sub-selects to see if they contain uses of
701-
*nonstrict functions. It's not real clear if that is correct or not...
702-
*forthecurrent usage it does not matter, since inline_function()
703-
*rejects cases with sublinks.
700+
*The idea here is that the caller has verified that the expression contains
701+
*one or more Var or Param nodes (as appropriate for the caller's need), and
702+
*now wishes to prove thattheexpression result will be NULL if any of these
703+
*inputs is NULL. If we return false, then the proof succeeded.
704704
*/
705705
bool
706706
contain_nonstrict_functions(Node*clause)
@@ -713,6 +713,11 @@ contain_nonstrict_functions_walker(Node *node, void *context)
713713
{
714714
if (node==NULL)
715715
return false;
716+
if (IsA(node,Aggref))
717+
{
718+
/* an aggregate could return non-null with null input */
719+
return true;
720+
}
716721
if (IsA(node,FuncExpr))
717722
{
718723
FuncExpr*expr= (FuncExpr*)node;
@@ -745,16 +750,25 @@ contain_nonstrict_functions_walker(Node *node, void *context)
745750

746751
switch (expr->boolop)
747752
{
748-
caseOR_EXPR:
749753
caseAND_EXPR:
750-
/* OR, AND are inherently non-strict */
754+
caseOR_EXPR:
755+
/* AND, OR are inherently non-strict */
751756
return true;
752757
default:
753758
break;
754759
}
755760
}
761+
if (IsA(node,SubLink))
762+
{
763+
/* In some cases a sublink might be strict, but in general not */
764+
return true;
765+
}
766+
if (IsA(node,SubPlan))
767+
return true;
756768
if (IsA(node,CaseExpr))
757769
return true;
770+
if (IsA(node,CaseWhen))
771+
return true;
758772
/* NB: ArrayExpr might someday be nonstrict */
759773
if (IsA(node,CoalesceExpr))
760774
return true;
@@ -764,18 +778,6 @@ contain_nonstrict_functions_walker(Node *node, void *context)
764778
return true;
765779
if (IsA(node,BooleanTest))
766780
return true;
767-
if (IsA(node,SubLink))
768-
{
769-
SubLink*sublink= (SubLink*)node;
770-
List*opid;
771-
772-
foreach(opid,sublink->operOids)
773-
{
774-
if (!op_strict(lfirsto(opid)))
775-
return true;
776-
}
777-
/* else fall through to check args */
778-
}
779781
returnexpression_tree_walker(node,contain_nonstrict_functions_walker,
780782
context);
781783
}

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