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Previous patch to mark UNION outputs with common typmod (if any) breaks
three-or-more-way UNIONs, as per example from Josh Berkus. Cause is a fragile assumption that one tlist's entries will exactly match another. Restructure code to make that assumption a little less fragile.
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‎src/backend/optimizer/prep/prepunion.c

Lines changed: 118 additions & 62 deletions
Original file line numberDiff line numberDiff line change
@@ -14,7 +14,7 @@
1414
*
1515
*
1616
* IDENTIFICATION
17-
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.70 2002/03/01 06:01:20 tgl Exp $
17+
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.71 2002/03/05 05:10:24 tgl Exp $
1818
*
1919
*-------------------------------------------------------------------------
2020
*/
@@ -63,7 +63,9 @@ static List *generate_setop_tlist(List *colTypes, int flag,
6363
bool hack_constants,
6464
List *input_tlist,
6565
List *refnames_tlist);
66-
static void merge_tlist_typmods(List *tlist, List *planlist);
66+
static List *generate_append_tlist(List *colTypes, bool flag,
67+
List *input_plans,
68+
List *refnames_tlist);
6769
static bool tlist_same_datatypes(List *tlist, List *colTypes, bool junkOK);
6870
static Node *adjust_inherited_attrs_mutator(Node *node,
6971
adjust_inherited_attrs_context *context);
@@ -169,13 +171,11 @@ recurse_set_operations(Node *setOp, Query *parse,
169171
*
170172
* XXX you don't really want to know about this: setrefs.c will apply
171173
* replace_vars_with_subplan_refs() to the Result node's tlist.
172-
* This would fail if the input plan's non-resjunk tlist entries
173-
* were not all simple Vars equal() to the referencing Vars
174-
* generated by generate_setop_tlist(). However, since the input
175-
* plan was generated by generate_union_plan() or
176-
* generate_nonunion_plan(), the referencing Vars will equal the
177-
* tlist entries they reference. Ugly but I don't feel like making
178-
* that code more general right now.
174+
* This would fail if the Vars generated by generate_setop_tlist()
175+
* were not exactly equal() to the corresponding tlist entries of
176+
* the subplan. However, since the subplan was generated by
177+
* generate_union_plan() or generate_nonunion_plan(), and hence its
178+
* tlist was generated by generate_append_tlist(), this will work.
179179
*/
180180
if (flag >= 0 ||
181181
!tlist_same_datatypes(plan->targetlist, colTypes, junkOK))
@@ -226,10 +226,8 @@ generate_union_plan(SetOperationStmt *op, Query *parse,
226226
* concerned, but we must make it look real anyway for the benefit of
227227
* the next plan level up.
228228
*/
229-
tlist = generate_setop_tlist(op->colTypes, -1, false,
230-
((Plan *) lfirst(planlist))->targetlist,
231-
refnames_tlist);
232-
merge_tlist_typmods(tlist, planlist);
229+
tlist = generate_append_tlist(op->colTypes, false,
230+
planlist, refnames_tlist);
233231

234232
/*
235233
* Append the child results together.
@@ -285,10 +283,8 @@ generate_nonunion_plan(SetOperationStmt *op, Query *parse,
285283
* flag column is shown as a variable not a constant, else setrefs.c
286284
* will get confused.
287285
*/
288-
tlist = generate_setop_tlist(op->colTypes, 2, false,
289-
lplan->targetlist,
290-
refnames_tlist);
291-
merge_tlist_typmods(tlist, planlist);
286+
tlist = generate_append_tlist(op->colTypes, true,
287+
planlist, refnames_tlist);
292288

293289
/*
294290
* Append the child results together.
@@ -368,8 +364,7 @@ recurse_union_children(Node *setOp, Query *parse,
368364
* Generate targetlist for a set-operation plan node
369365
*
370366
* colTypes: column datatypes for non-junk columns
371-
* flag: -1 if no flag column needed, 0 or 1 to create a const flag column,
372-
* 2 to create a variable flag column
367+
* flag: -1 if no flag column needed, 0 or 1 to create a const flag column
373368
* hack_constants: true to copy up constants (see comments in code)
374369
* input_tlist: targetlist of this node's input node
375370
* refnames_tlist: targetlist to take column names from
@@ -450,71 +445,132 @@ generate_setop_tlist(List *colTypes, int flag,
450445
-1,
451446
pstrdup("flag"),
452447
true);
453-
if (flag <= 1)
454-
{
455-
/* flag value is the given constant */
456-
expr = (Node *) makeConst(INT4OID,
457-
sizeof(int4),
458-
Int32GetDatum(flag),
459-
false,
460-
true,
461-
false,
462-
false);
463-
}
464-
else
465-
{
466-
/* flag value is being copied up from subplan */
467-
expr = (Node *) makeVar(0,
468-
resdom->resno,
469-
INT4OID,
470-
-1,
471-
0);
472-
}
448+
/* flag value is the given constant */
449+
expr = (Node *) makeConst(INT4OID,
450+
sizeof(int4),
451+
Int32GetDatum(flag),
452+
false,
453+
true,
454+
false,
455+
false);
473456
tlist = lappend(tlist, makeTargetEntry(resdom, expr));
474457
}
475458

476459
return tlist;
477460
}
478461

479462
/*
480-
* Merge typmods of a list of set-operation subplans.
463+
* Generate targetlist for a set-operation Append node
464+
*
465+
* colTypes: column datatypes for non-junk columns
466+
* flag: true to create a flag column copied up from subplans
467+
* input_plans: list of sub-plans of the Append
468+
* refnames_tlist: targetlist to take column names from
481469
*
482-
* If the inputs all agree on type and typmod of a particular column,
483-
* use that typmod; else use -1. We assume the result tlist has been
484-
* initialized with the types and typmods of the first input subplan.
470+
* The entries in the Append's targetlist should always be simple Vars;
471+
* we just have to make sure they have the right datatypes and typmods.
485472
*/
486-
static void
487-
merge_tlist_typmods(List *tlist, List *planlist)
473+
static List *
474+
generate_append_tlist(List *colTypes, bool flag,
475+
List *input_plans,
476+
List *refnames_tlist)
488477
{
478+
List *tlist = NIL;
479+
int resno = 1;
480+
List *curColType;
481+
int colindex;
482+
Resdom *resdom;
483+
Node *expr;
489484
List *planl;
485+
int32 *colTypmods;
486+
487+
/*
488+
* First extract typmods to use.
489+
*
490+
* If the inputs all agree on type and typmod of a particular column,
491+
* use that typmod; else use -1.
492+
*/
493+
colTypmods = (int32 *) palloc(length(colTypes) * sizeof(int32));
490494

491-
foreach(planl, planlist)
495+
foreach(planl, input_plans)
492496
{
493497
Plan *subplan = (Plan *) lfirst(planl);
494-
List *subtlist = subplan->targetlist;
495-
List *restlist;
498+
List *subtlist;
496499

497-
foreach(restlist, tlist)
500+
curColType = colTypes;
501+
colindex = 0;
502+
foreach(subtlist, subplan->targetlist)
498503
{
499-
TargetEntry *restle = (TargetEntry *) lfirst(restlist);
500-
TargetEntry *subtle;
504+
TargetEntry *subtle = (TargetEntry *) lfirst(subtlist);
501505

502-
if (restle->resdom->resjunk)
506+
if (subtle->resdom->resjunk)
503507
continue;
504-
Assert(subtlist != NIL);
505-
subtle = (TargetEntry *) lfirst(subtlist);
506-
while (subtle->resdom->resjunk)
508+
Assert(curColType != NIL);
509+
if (subtle->resdom->restype == (Oid) lfirsti(curColType))
507510
{
508-
subtlist = lnext(subtlist);
509-
Assert(subtlist != NIL);
510-
subtle = (TargetEntry *) lfirst(subtlist);
511+
/* If first subplan, copy the typmod; else compare */
512+
if (planl == input_plans)
513+
colTypmods[colindex] = subtle->resdom->restypmod;
514+
else if (subtle->resdom->restypmod != colTypmods[colindex])
515+
colTypmods[colindex] = -1;
511516
}
512-
if (restle->resdom->restype != subtle->resdom->restype ||
513-
restle->resdom->restypmod != subtle->resdom->restypmod)
514-
restle->resdom->restypmod = -1;
515-
subtlist = lnext(subtlist);
517+
else
518+
{
519+
/* types disagree, so force typmod to -1 */
520+
colTypmods[colindex] = -1;
521+
}
522+
curColType = lnext(curColType);
523+
colindex++;
516524
}
525+
Assert(curColType == NIL);
517526
}
527+
528+
/*
529+
* Now we can build the tlist for the Append.
530+
*/
531+
colindex = 0;
532+
foreach(curColType, colTypes)
533+
{
534+
Oid colType = (Oid) lfirsti(curColType);
535+
int32 colTypmod = colTypmods[colindex++];
536+
TargetEntry *reftle = (TargetEntry *) lfirst(refnames_tlist);
537+
538+
Assert(reftle->resdom->resno == resno);
539+
Assert(!reftle->resdom->resjunk);
540+
expr = (Node *) makeVar(0,
541+
resno,
542+
colType,
543+
colTypmod,
544+
0);
545+
resdom = makeResdom((AttrNumber) resno++,
546+
colType,
547+
colTypmod,
548+
pstrdup(reftle->resdom->resname),
549+
false);
550+
tlist = lappend(tlist, makeTargetEntry(resdom, expr));
551+
refnames_tlist = lnext(refnames_tlist);
552+
}
553+
554+
if (flag)
555+
{
556+
/* Add a resjunk flag column */
557+
resdom = makeResdom((AttrNumber) resno++,
558+
INT4OID,
559+
-1,
560+
pstrdup("flag"),
561+
true);
562+
/* flag value is shown as copied up from subplan */
563+
expr = (Node *) makeVar(0,
564+
resdom->resno,
565+
INT4OID,
566+
-1,
567+
0);
568+
tlist = lappend(tlist, makeTargetEntry(resdom, expr));
569+
}
570+
571+
pfree(colTypmods);
572+
573+
return tlist;
518574
}
519575

520576
/*

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