1/*-------------------------------------------------------------------------
2 *
3 * parse_collate.c
4 * Routines for assigning collation information.
5 *
6 * We choose to handle collation analysis in a post-pass over the output
7 * of expression parse analysis. This is because we need more state to
8 * perform this processing than is needed in the finished tree. If we
9 * did it on-the-fly while building the tree, all that state would have
10 * to be kept in expression node trees permanently. This way, the extra
11 * storage is just local variables in this recursive routine.
12 *
13 * The info that is actually saved in the finished tree is:
14 * 1. The output collation of each expression node, or InvalidOid if it
15 * returns a noncollatable data type. This can also be InvalidOid if the
16 * result type is collatable but the collation is indeterminate.
17 * 2. The collation to be used in executing each function. InvalidOid means
18 * that there are no collatable inputs or their collation is indeterminate.
19 * This value is only stored in node types that might call collation-using
20 * functions.
21 *
22 * You might think we could get away with storing only one collation per
23 * node, but the two concepts really need to be kept distinct. Otherwise
24 * it's too confusing when a function produces a collatable output type but
25 * has no collatable inputs or produces noncollatable output from collatable
26 * inputs.
27 *
28 * Cases with indeterminate collation might result in an error being thrown
29 * at runtime. If we knew exactly which functions require collation
30 * information, we could throw those errors at parse time instead.
31 *
32 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
33 * Portions Copyright (c) 1994, Regents of the University of California
34 *
35 *
36 * IDENTIFICATION
37 * src/backend/parser/parse_collate.c
38 *
39 *-------------------------------------------------------------------------
40 */
41#include "postgres.h"
42
43#include "catalog/pg_aggregate.h"
44#include "catalog/pg_collation.h"
45#include "nodes/makefuncs.h"
46#include "nodes/nodeFuncs.h"
47#include "parser/parse_collate.h"
48#include "utils/lsyscache.h"
49
50
51/*
52 * Collation strength (the SQL standard calls this "derivation"). Order is
53 * chosen to allow comparisons to work usefully. Note: the standard doesn't
54 * seem to distinguish between NONE and CONFLICT.
55 */
56typedef enum
57{
58 COLLATE_NONE, /* expression is of a noncollatable datatype */
59 COLLATE_IMPLICIT, /* collation was derived implicitly */
60 COLLATE_CONFLICT, /* we had a conflict of implicit collations */
61 COLLATE_EXPLICIT /* collation was derived explicitly */
62} CollateStrength;
63
64typedef struct
65{
66 ParseState *pstate; /* parse state (for error reporting) */
67 Oid collation; /* OID of current collation, if any */
68 CollateStrength strength; /* strength of current collation choice */
69 int location; /* location of expr that set collation */
70 /* Remaining fields are only valid when strength == COLLATE_CONFLICT */
71 Oid collation2; /* OID of conflicting collation */
72 int location2; /* location of expr that set collation2 */
73} assign_collations_context;
74
75static bool assign_query_collations_walker(Node *node, ParseState *pstate);
76static bool assign_collations_walker(Node *node,
77 assign_collations_context *context);
78static void merge_collation_state(Oid collation,
79 CollateStrength strength,
80 int location,
81 Oid collation2,
82 int location2,
83 assign_collations_context *context);
84static void assign_aggregate_collations(Aggref *aggref,
85 assign_collations_context *loccontext);
86static void assign_ordered_set_collations(Aggref *aggref,
87 assign_collations_context *loccontext);
88static void assign_hypothetical_collations(Aggref *aggref,
89 assign_collations_context *loccontext);
90
91
92/*
93 * assign_query_collations()
94 * Mark all expressions in the given Query with collation information.
95 *
96 * This should be applied to each Query after completion of parse analysis
97 * for expressions. Note that we do not recurse into sub-Queries, since
98 * those should have been processed when built.
99 */
100void
101assign_query_collations(ParseState *pstate, Query *query)
102{
103 /*
104 * We just use query_tree_walker() to visit all the contained expressions.
105 * We can skip the rangetable and CTE subqueries, though, since RTEs and
106 * subqueries had better have been processed already (else Vars referring
107 * to them would not get created with the right collation).
108 */
109 (void) query_tree_walker(query,
110 assign_query_collations_walker,
111 (void *) pstate,
112 QTW_IGNORE_RANGE_TABLE |
113 QTW_IGNORE_CTE_SUBQUERIES);
114}
115
116/*
117 * Walker for assign_query_collations
118 *
119 * Each expression found by query_tree_walker is processed independently.
120 * Note that query_tree_walker may pass us a whole List, such as the
121 * targetlist, in which case each subexpression must be processed
122 * independently --- we don't want to bleat if two different targetentries
123 * have different collations.
124 */
125static bool
126assign_query_collations_walker(Node *node, ParseState *pstate)
127{
128 /* Need do nothing for empty subexpressions */
129 if (node == NULL)
130 return false;
131
132 /*
133 * We don't want to recurse into a set-operations tree; it's already been
134 * fully processed in transformSetOperationStmt.
135 */
136 if (IsA(node, SetOperationStmt))
137 return false;
138
139 if (IsA(node, List))
140 assign_list_collations(pstate, (List *) node);
141 else
142 assign_expr_collations(pstate, node);
143
144 return false;
145}
146
147/*
148 * assign_list_collations()
149 * Mark all nodes in the list of expressions with collation information.
150 *
151 * The list member expressions are processed independently; they do not have
152 * to share a common collation.
153 */
154void
155assign_list_collations(ParseState *pstate, List *exprs)
156{
157 ListCell *lc;
158
159 foreach(lc, exprs)
160 {
161 Node *node = (Node *) lfirst(lc);
162
163 assign_expr_collations(pstate, node);
164 }
165}
166
167/*
168 * assign_expr_collations()
169 * Mark all nodes in the given expression tree with collation information.
170 *
171 * This is exported for the benefit of various utility commands that process
172 * expressions without building a complete Query. It should be applied after
173 * calling transformExpr() plus any expression-modifying operations such as
174 * coerce_to_boolean().
175 */
176void
177assign_expr_collations(ParseState *pstate, Node *expr)
178{
179 assign_collations_context context;
180
181 /* initialize context for tree walk */
182 context.pstate = pstate;
183 context.collation = InvalidOid;
184 context.strength = COLLATE_NONE;
185 context.location = -1;
186
187 /* and away we go */
188 (void) assign_collations_walker(expr, &context);
189}
190
191/*
192 * select_common_collation()
193 * Identify a common collation for a list of expressions.
194 *
195 * The expressions should all return the same datatype, else this is not
196 * terribly meaningful.
197 *
198 * none_ok means that it is permitted to return InvalidOid, indicating that
199 * no common collation could be identified, even for collatable datatypes.
200 * Otherwise, an error is thrown for conflict of implicit collations.
201 *
202 * In theory, none_ok = true reflects the rules of SQL standard clause "Result
203 * of data type combinations", none_ok = false reflects the rules of clause
204 * "Collation determination" (in some cases invoked via "Grouping
205 * operations").
206 */
207Oid
208select_common_collation(ParseState *pstate, List *exprs, bool none_ok)
209{
210 assign_collations_context context;
211
212 /* initialize context for tree walk */
213 context.pstate = pstate;
214 context.collation = InvalidOid;
215 context.strength = COLLATE_NONE;
216 context.location = -1;
217
218 /* and away we go */
219 (void) assign_collations_walker((Node *) exprs, &context);
220
221 /* deal with collation conflict */
222 if (context.strength == COLLATE_CONFLICT)
223 {
224 if (none_ok)
225 return InvalidOid;
226 ereport(ERROR,
227 (errcode(ERRCODE_COLLATION_MISMATCH),
228 errmsg("collation mismatch between implicit collations \"%s\" and \"%s\"",
229 get_collation_name(context.collation),
230 get_collation_name(context.collation2)),
231 errhint("You can choose the collation by applying the COLLATE clause to one or both expressions."),
232 parser_errposition(context.pstate, context.location2)));
233 }
234
235 /*
236 * Note: if strength is still COLLATE_NONE, we'll return InvalidOid, but
237 * that's okay because it must mean none of the expressions returned
238 * collatable datatypes.
239 */
240 return context.collation;
241}
242
243/*
244 * assign_collations_walker()
245 * Recursive guts of collation processing.
246 *
247 * Nodes with no children (eg, Vars, Consts, Params) must have been marked
248 * when built. All upper-level nodes are marked here.
249 *
250 * Note: if this is invoked directly on a List, it will attempt to infer a
251 * common collation for all the list members. In particular, it will throw
252 * error if there are conflicting explicit collations for different members.
253 */
254static bool
255assign_collations_walker(Node *node, assign_collations_context *context)
256{
257 assign_collations_context loccontext;
258 Oid collation;
259 CollateStrength strength;
260 int location;
261
262 /* Need do nothing for empty subexpressions */
263 if (node == NULL)
264 return false;
265
266 /*
267 * Prepare for recursion. For most node types, though not all, the first
268 * thing we do is recurse to process all nodes below this one. Each level
269 * of the tree has its own local context.
270 */
271 loccontext.pstate = context->pstate;
272 loccontext.collation = InvalidOid;
273 loccontext.strength = COLLATE_NONE;
274 loccontext.location = -1;
275 /* Set these fields just to suppress uninitialized-value warnings: */
276 loccontext.collation2 = InvalidOid;
277 loccontext.location2 = -1;
278
279 /*
280 * Recurse if appropriate, then determine the collation for this node.
281 *
282 * Note: the general cases are at the bottom of the switch, after various
283 * special cases.
284 */
285 switch (nodeTag(node))
286 {
287 case T_CollateExpr:
288 {
289 /*
290 * COLLATE sets an explicitly derived collation, regardless of
291 * what the child state is. But we must recurse to set up
292 * collation info below here.
293 */
294 CollateExpr *expr = (CollateExpr *) node;
295
296 (void) expression_tree_walker(node,
297 assign_collations_walker,
298 (void *) &loccontext);
299
300 collation = expr->collOid;
301 Assert(OidIsValid(collation));
302 strength = COLLATE_EXPLICIT;
303 location = expr->location;
304 }
305 break;
306 case T_FieldSelect:
307 {
308 /*
309 * For FieldSelect, the result has the field's declared
310 * collation, independently of what happened in the arguments.
311 * (The immediate argument must be composite and thus not
312 * collatable, anyhow.) The field's collation was already
313 * looked up and saved in the node.
314 */
315 FieldSelect *expr = (FieldSelect *) node;
316
317 /* ... but first, recurse */
318 (void) expression_tree_walker(node,
319 assign_collations_walker,
320 (void *) &loccontext);
321
322 if (OidIsValid(expr->resultcollid))
323 {
324 /* Node's result type is collatable. */
325 /* Pass up field's collation as an implicit choice. */
326 collation = expr->resultcollid;
327 strength = COLLATE_IMPLICIT;
328 location = exprLocation(node);
329 }
330 else
331 {
332 /* Node's result type isn't collatable. */
333 collation = InvalidOid;
334 strength = COLLATE_NONE;
335 location = -1; /* won't be used */
336 }
337 }
338 break;
339 case T_RowExpr:
340 {
341 /*
342 * RowExpr is a special case because the subexpressions are
343 * independent: we don't want to complain if some of them have
344 * incompatible explicit collations.
345 */
346 RowExpr *expr = (RowExpr *) node;
347
348 assign_list_collations(context->pstate, expr->args);
349
350 /*
351 * Since the result is always composite and therefore never
352 * has a collation, we can just stop here: this node has no
353 * impact on the collation of its parent.
354 */
355 return false; /* done */
356 }
357 case T_RowCompareExpr:
358 {
359 /*
360 * For RowCompare, we have to find the common collation of
361 * each pair of input columns and build a list. If we can't
362 * find a common collation, we just put InvalidOid into the
363 * list, which may or may not cause an error at runtime.
364 */
365 RowCompareExpr *expr = (RowCompareExpr *) node;
366 List *colls = NIL;
367 ListCell *l;
368 ListCell *r;
369
370 forboth(l, expr->largs, r, expr->rargs)
371 {
372 Node *le = (Node *) lfirst(l);
373 Node *re = (Node *) lfirst(r);
374 Oid coll;
375
376 coll = select_common_collation(context->pstate,
377 list_make2(le, re),
378 true);
379 colls = lappend_oid(colls, coll);
380 }
381 expr->inputcollids = colls;
382
383 /*
384 * Since the result is always boolean and therefore never has
385 * a collation, we can just stop here: this node has no impact
386 * on the collation of its parent.
387 */
388 return false; /* done */
389 }
390 case T_CoerceToDomain:
391 {
392 /*
393 * If the domain declaration included a non-default COLLATE
394 * spec, then use that collation as the output collation of
395 * the coercion. Otherwise allow the input collation to
396 * bubble up. (The input should be of the domain's base type,
397 * therefore we don't need to worry about it not being
398 * collatable when the domain is.)
399 */
400 CoerceToDomain *expr = (CoerceToDomain *) node;
401 Oid typcollation = get_typcollation(expr->resulttype);
402
403 /* ... but first, recurse */
404 (void) expression_tree_walker(node,
405 assign_collations_walker,
406 (void *) &loccontext);
407
408 if (OidIsValid(typcollation))
409 {
410 /* Node's result type is collatable. */
411 if (typcollation == DEFAULT_COLLATION_OID)
412 {
413 /* Collation state bubbles up from child. */
414 collation = loccontext.collation;
415 strength = loccontext.strength;
416 location = loccontext.location;
417 }
418 else
419 {
420 /* Use domain's collation as an implicit choice. */
421 collation = typcollation;
422 strength = COLLATE_IMPLICIT;
423 location = exprLocation(node);
424 }
425 }
426 else
427 {
428 /* Node's result type isn't collatable. */
429 collation = InvalidOid;
430 strength = COLLATE_NONE;
431 location = -1; /* won't be used */
432 }
433
434 /*
435 * Save the state into the expression node. We know it
436 * doesn't care about input collation.
437 */
438 if (strength == COLLATE_CONFLICT)
439 exprSetCollation(node, InvalidOid);
440 else
441 exprSetCollation(node, collation);
442 }
443 break;
444 case T_TargetEntry:
445 (void) expression_tree_walker(node,
446 assign_collations_walker,
447 (void *) &loccontext);
448
449 /*
450 * TargetEntry can have only one child, and should bubble that
451 * state up to its parent. We can't use the general-case code
452 * below because exprType and friends don't work on TargetEntry.
453 */
454 collation = loccontext.collation;
455 strength = loccontext.strength;
456 location = loccontext.location;
457
458 /*
459 * Throw error if the collation is indeterminate for a TargetEntry
460 * that is a sort/group target. We prefer to do this now, instead
461 * of leaving the comparison functions to fail at runtime, because
462 * we can give a syntax error pointer to help locate the problem.
463 * There are some cases where there might not be a failure, for
464 * example if the planner chooses to use hash aggregation instead
465 * of sorting for grouping; but it seems better to predictably
466 * throw an error. (Compare transformSetOperationTree, which will
467 * throw error for indeterminate collation of set-op columns, even
468 * though the planner might be able to implement the set-op
469 * without sorting.)
470 */
471 if (strength == COLLATE_CONFLICT &&
472 ((TargetEntry *) node)->ressortgroupref != 0)
473 ereport(ERROR,
474 (errcode(ERRCODE_COLLATION_MISMATCH),
475 errmsg("collation mismatch between implicit collations \"%s\" and \"%s\"",
476 get_collation_name(loccontext.collation),
477 get_collation_name(loccontext.collation2)),
478 errhint("You can choose the collation by applying the COLLATE clause to one or both expressions."),
479 parser_errposition(context->pstate,
480 loccontext.location2)));
481 break;
482 case T_InferenceElem:
483 case T_RangeTblRef:
484 case T_JoinExpr:
485 case T_FromExpr:
486 case T_OnConflictExpr:
487 case T_SortGroupClause:
488 (void) expression_tree_walker(node,
489 assign_collations_walker,
490 (void *) &loccontext);
491
492 /*
493 * When we're invoked on a query's jointree, we don't need to do
494 * anything with join nodes except recurse through them to process
495 * WHERE/ON expressions. So just stop here. Likewise, we don't
496 * need to do anything when invoked on sort/group lists.
497 */
498 return false;
499 case T_Query:
500 {
501 /*
502 * We get here when we're invoked on the Query belonging to a
503 * SubLink. Act as though the Query returns its first output
504 * column, which indeed is what it does for EXPR_SUBLINK and
505 * ARRAY_SUBLINK cases. In the cases where the SubLink
506 * returns boolean, this info will be ignored. Special case:
507 * in EXISTS, the Query might return no columns, in which case
508 * we need do nothing.
509 *
510 * We needn't recurse, since the Query is already processed.
511 */
512 Query *qtree = (Query *) node;
513 TargetEntry *tent;
514
515 if (qtree->targetList == NIL)
516 return false;
517 tent = linitial_node(TargetEntry, qtree->targetList);
518 if (tent->resjunk)
519 return false;
520
521 collation = exprCollation((Node *) tent->expr);
522 /* collation doesn't change if it's converted to array */
523 strength = COLLATE_IMPLICIT;
524 location = exprLocation((Node *) tent->expr);
525 }
526 break;
527 case T_List:
528 (void) expression_tree_walker(node,
529 assign_collations_walker,
530 (void *) &loccontext);
531
532 /*
533 * When processing a list, collation state just bubbles up from
534 * the list elements.
535 */
536 collation = loccontext.collation;
537 strength = loccontext.strength;
538 location = loccontext.location;
539 break;
540
541 case T_Var:
542 case T_Const:
543 case T_Param:
544 case T_CoerceToDomainValue:
545 case T_CaseTestExpr:
546 case T_SetToDefault:
547 case T_CurrentOfExpr:
548
549 /*
550 * General case for childless expression nodes. These should
551 * already have a collation assigned; it is not this function's
552 * responsibility to look into the catalogs for base-case
553 * information.
554 */
555 collation = exprCollation(node);
556
557 /*
558 * Note: in most cases, there will be an assigned collation
559 * whenever type_is_collatable(exprType(node)); but an exception
560 * occurs for a Var referencing a subquery output column for which
561 * a unique collation was not determinable. That may lead to a
562 * runtime failure if a collation-sensitive function is applied to
563 * the Var.
564 */
565
566 if (OidIsValid(collation))
567 strength = COLLATE_IMPLICIT;
568 else
569 strength = COLLATE_NONE;
570 location = exprLocation(node);
571 break;
572
573 default:
574 {
575 /*
576 * General case for most expression nodes with children. First
577 * recurse, then figure out what to assign to this node.
578 */
579 Oid typcollation;
580
581 /*
582 * For most node types, we want to treat all the child
583 * expressions alike; but there are a few exceptions, hence
584 * this inner switch.
585 */
586 switch (nodeTag(node))
587 {
588 case T_Aggref:
589 {
590 /*
591 * Aggref is messy enough that we give it its own
592 * function, in fact three of them. The FILTER
593 * clause is independent of the rest of the
594 * aggregate, however, so it can be processed
595 * separately.
596 */
597 Aggref *aggref = (Aggref *) node;
598
599 switch (aggref->aggkind)
600 {
601 case AGGKIND_NORMAL:
602 assign_aggregate_collations(aggref,
603 &loccontext);
604 break;
605 case AGGKIND_ORDERED_SET:
606 assign_ordered_set_collations(aggref,
607 &loccontext);
608 break;
609 case AGGKIND_HYPOTHETICAL:
610 assign_hypothetical_collations(aggref,
611 &loccontext);
612 break;
613 default:
614 elog(ERROR, "unrecognized aggkind: %d",
615 (int) aggref->aggkind);
616 }
617
618 assign_expr_collations(context->pstate,
619 (Node *) aggref->aggfilter);
620 }
621 break;
622 case T_WindowFunc:
623 {
624 /*
625 * WindowFunc requires special processing only for
626 * its aggfilter clause, as for aggregates.
627 */
628 WindowFunc *wfunc = (WindowFunc *) node;
629
630 (void) assign_collations_walker((Node *) wfunc->args,
631 &loccontext);
632
633 assign_expr_collations(context->pstate,
634 (Node *) wfunc->aggfilter);
635 }
636 break;
637 case T_CaseExpr:
638 {
639 /*
640 * CaseExpr is a special case because we do not
641 * want to recurse into the test expression (if
642 * any). It was already marked with collations
643 * during transformCaseExpr, and furthermore its
644 * collation is not relevant to the result of the
645 * CASE --- only the output expressions are.
646 */
647 CaseExpr *expr = (CaseExpr *) node;
648 ListCell *lc;
649
650 foreach(lc, expr->args)
651 {
652 CaseWhen *when = lfirst_node(CaseWhen, lc);
653
654 /*
655 * The condition expressions mustn't affect
656 * the CASE's result collation either; but
657 * since they are known to yield boolean, it's
658 * safe to recurse directly on them --- they
659 * won't change loccontext.
660 */
661 (void) assign_collations_walker((Node *) when->expr,
662 &loccontext);
663 (void) assign_collations_walker((Node *) when->result,
664 &loccontext);
665 }
666 (void) assign_collations_walker((Node *) expr->defresult,
667 &loccontext);
668 }
669 break;
670 default:
671
672 /*
673 * Normal case: all child expressions contribute
674 * equally to loccontext.
675 */
676 (void) expression_tree_walker(node,
677 assign_collations_walker,
678 (void *) &loccontext);
679 break;
680 }
681
682 /*
683 * Now figure out what collation to assign to this node.
684 */
685 typcollation = get_typcollation(exprType(node));
686 if (OidIsValid(typcollation))
687 {
688 /* Node's result is collatable; what about its input? */
689 if (loccontext.strength > COLLATE_NONE)
690 {
691 /* Collation state bubbles up from children. */
692 collation = loccontext.collation;
693 strength = loccontext.strength;
694 location = loccontext.location;
695 }
696 else
697 {
698 /*
699 * Collatable output produced without any collatable
700 * input. Use the type's collation (which is usually
701 * DEFAULT_COLLATION_OID, but might be different for a
702 * domain).
703 */
704 collation = typcollation;
705 strength = COLLATE_IMPLICIT;
706 location = exprLocation(node);
707 }
708 }
709 else
710 {
711 /* Node's result type isn't collatable. */
712 collation = InvalidOid;
713 strength = COLLATE_NONE;
714 location = -1; /* won't be used */
715 }
716
717 /*
718 * Save the result collation into the expression node. If the
719 * state is COLLATE_CONFLICT, we'll set the collation to
720 * InvalidOid, which might result in an error at runtime.
721 */
722 if (strength == COLLATE_CONFLICT)
723 exprSetCollation(node, InvalidOid);
724 else
725 exprSetCollation(node, collation);
726
727 /*
728 * Likewise save the input collation, which is the one that
729 * any function called by this node should use.
730 */
731 if (loccontext.strength == COLLATE_CONFLICT)
732 exprSetInputCollation(node, InvalidOid);
733 else
734 exprSetInputCollation(node, loccontext.collation);
735 }
736 break;
737 }
738
739 /*
740 * Now, merge my information into my parent's state.
741 */
742 merge_collation_state(collation,
743 strength,
744 location,
745 loccontext.collation2,
746 loccontext.location2,
747 context);
748
749 return false;
750}
751
752/*
753 * Merge collation state of a subexpression into the context for its parent.
754 */
755static void
756merge_collation_state(Oid collation,
757 CollateStrength strength,
758 int location,
759 Oid collation2,
760 int location2,
761 assign_collations_context *context)
762{
763 /*
764 * If the collation strength for this node is different from what's
765 * already in *context, then this node either dominates or is dominated by
766 * earlier siblings.
767 */
768 if (strength > context->strength)
769 {
770 /* Override previous parent state */
771 context->collation = collation;
772 context->strength = strength;
773 context->location = location;
774 /* Bubble up error info if applicable */
775 if (strength == COLLATE_CONFLICT)
776 {
777 context->collation2 = collation2;
778 context->location2 = location2;
779 }
780 }
781 else if (strength == context->strength)
782 {
783 /* Merge, or detect error if there's a collation conflict */
784 switch (strength)
785 {
786 case COLLATE_NONE:
787 /* Nothing + nothing is still nothing */
788 break;
789 case COLLATE_IMPLICIT:
790 if (collation != context->collation)
791 {
792 /*
793 * Non-default implicit collation always beats default.
794 */
795 if (context->collation == DEFAULT_COLLATION_OID)
796 {
797 /* Override previous parent state */
798 context->collation = collation;
799 context->strength = strength;
800 context->location = location;
801 }
802 else if (collation != DEFAULT_COLLATION_OID)
803 {
804 /*
805 * Oops, we have a conflict. We cannot throw error
806 * here, since the conflict could be resolved by a
807 * later sibling CollateExpr, or the parent might not
808 * care about collation anyway. Return enough info to
809 * throw the error later, if needed.
810 */
811 context->strength = COLLATE_CONFLICT;
812 context->collation2 = collation;
813 context->location2 = location;
814 }
815 }
816 break;
817 case COLLATE_CONFLICT:
818 /* We're still conflicted ... */
819 break;
820 case COLLATE_EXPLICIT:
821 if (collation != context->collation)
822 {
823 /*
824 * Oops, we have a conflict of explicit COLLATE clauses.
825 * Here we choose to throw error immediately; that is what
826 * the SQL standard says to do, and there's no good reason
827 * to be less strict.
828 */
829 ereport(ERROR,
830 (errcode(ERRCODE_COLLATION_MISMATCH),
831 errmsg("collation mismatch between explicit collations \"%s\" and \"%s\"",
832 get_collation_name(context->collation),
833 get_collation_name(collation)),
834 parser_errposition(context->pstate, location)));
835 }
836 break;
837 }
838 }
839}
840
841/*
842 * Aggref is a special case because expressions used only for ordering
843 * shouldn't be taken to conflict with each other or with regular args,
844 * indeed shouldn't affect the aggregate's result collation at all.
845 * We handle this by applying assign_expr_collations() to them rather than
846 * passing down our loccontext.
847 *
848 * Note that we recurse to each TargetEntry, not directly to its contained
849 * expression, so that the case above for T_TargetEntry will complain if we
850 * can't resolve a collation for an ORDER BY item (whether or not it is also
851 * a normal aggregate arg).
852 *
853 * We need not recurse into the aggorder or aggdistinct lists, because those
854 * contain only SortGroupClause nodes which we need not process.
855 */
856static void
857assign_aggregate_collations(Aggref *aggref,
858 assign_collations_context *loccontext)
859{
860 ListCell *lc;
861
862 /* Plain aggregates have no direct args */
863 Assert(aggref->aggdirectargs == NIL);
864
865 /* Process aggregated args, holding resjunk ones at arm's length */
866 foreach(lc, aggref->args)
867 {
868 TargetEntry *tle = lfirst_node(TargetEntry, lc);
869
870 if (tle->resjunk)
871 assign_expr_collations(loccontext->pstate, (Node *) tle);
872 else
873 (void) assign_collations_walker((Node *) tle, loccontext);
874 }
875}
876
877/*
878 * For ordered-set aggregates, it's somewhat unclear how best to proceed.
879 * The spec-defined inverse distribution functions have only one sort column
880 * and don't return collatable types, but this is clearly too restrictive in
881 * the general case. Our solution is to consider that the aggregate's direct
882 * arguments contribute normally to determination of the aggregate's own
883 * collation, while aggregated arguments contribute only when the aggregate
884 * is designed to have exactly one aggregated argument (i.e., it has a single
885 * aggregated argument and is non-variadic). If it can have more than one
886 * aggregated argument, we process the aggregated arguments as independent
887 * sort columns. This avoids throwing error for something like
888 * agg(...) within group (order by x collate "foo", y collate "bar")
889 * while also guaranteeing that variadic aggregates don't change in behavior
890 * depending on how many sort columns a particular call happens to have.
891 *
892 * Otherwise this is much like the plain-aggregate case.
893 */
894static void
895assign_ordered_set_collations(Aggref *aggref,
896 assign_collations_context *loccontext)
897{
898 bool merge_sort_collations;
899 ListCell *lc;
900
901 /* Merge sort collations to parent only if there can be only one */
902 merge_sort_collations = (list_length(aggref->args) == 1 &&
903 get_func_variadictype(aggref->aggfnoid) == InvalidOid);
904
905 /* Direct args, if any, are normal children of the Aggref node */
906 (void) assign_collations_walker((Node *) aggref->aggdirectargs,
907 loccontext);
908
909 /* Process aggregated args appropriately */
910 foreach(lc, aggref->args)
911 {
912 TargetEntry *tle = lfirst_node(TargetEntry, lc);
913
914 if (merge_sort_collations)
915 (void) assign_collations_walker((Node *) tle, loccontext);
916 else
917 assign_expr_collations(loccontext->pstate, (Node *) tle);
918 }
919}
920
921/*
922 * Hypothetical-set aggregates are even more special: per spec, we need to
923 * unify the collations of each pair of hypothetical and aggregated args.
924 * And we need to force the choice of collation down into the sort column
925 * to ensure that the sort happens with the chosen collation. Other than
926 * that, the behavior is like regular ordered-set aggregates. Note that
927 * hypothetical direct arguments contribute to the aggregate collation
928 * only when their partner aggregated arguments do.
929 */
930static void
931assign_hypothetical_collations(Aggref *aggref,
932 assign_collations_context *loccontext)
933{
934 ListCell *h_cell = list_head(aggref->aggdirectargs);
935 ListCell *s_cell = list_head(aggref->args);
936 bool merge_sort_collations;
937 int extra_args;
938
939 /* Merge sort collations to parent only if there can be only one */
940 merge_sort_collations = (list_length(aggref->args) == 1 &&
941 get_func_variadictype(aggref->aggfnoid) == InvalidOid);
942
943 /* Process any non-hypothetical direct args */
944 extra_args = list_length(aggref->aggdirectargs) - list_length(aggref->args);
945 Assert(extra_args >= 0);
946 while (extra_args-- > 0)
947 {
948 (void) assign_collations_walker((Node *) lfirst(h_cell), loccontext);
949 h_cell = lnext(h_cell);
950 }
951
952 /* Scan hypothetical args and aggregated args in parallel */
953 while (h_cell && s_cell)
954 {
955 Node *h_arg = (Node *) lfirst(h_cell);
956 TargetEntry *s_tle = (TargetEntry *) lfirst(s_cell);
957 assign_collations_context paircontext;
958
959 /*
960 * Assign collations internally in this pair of expressions, then
961 * choose a common collation for them. This should match
962 * select_common_collation(), but we can't use that function as-is
963 * because we need access to the whole collation state so we can
964 * bubble it up to the aggregate function's level.
965 */
966 paircontext.pstate = loccontext->pstate;
967 paircontext.collation = InvalidOid;
968 paircontext.strength = COLLATE_NONE;
969 paircontext.location = -1;
970 /* Set these fields just to suppress uninitialized-value warnings: */
971 paircontext.collation2 = InvalidOid;
972 paircontext.location2 = -1;
973
974 (void) assign_collations_walker(h_arg, &paircontext);
975 (void) assign_collations_walker((Node *) s_tle->expr, &paircontext);
976
977 /* deal with collation conflict */
978 if (paircontext.strength == COLLATE_CONFLICT)
979 ereport(ERROR,
980 (errcode(ERRCODE_COLLATION_MISMATCH),
981 errmsg("collation mismatch between implicit collations \"%s\" and \"%s\"",
982 get_collation_name(paircontext.collation),
983 get_collation_name(paircontext.collation2)),
984 errhint("You can choose the collation by applying the COLLATE clause to one or both expressions."),
985 parser_errposition(paircontext.pstate,
986 paircontext.location2)));
987
988 /*
989 * At this point paircontext.collation can be InvalidOid only if the
990 * type is not collatable; no need to do anything in that case. If we
991 * do have to change the sort column's collation, do it by inserting a
992 * RelabelType node into the sort column TLE.
993 *
994 * XXX This is pretty grotty for a couple of reasons:
995 * assign_collations_walker isn't supposed to be changing the
996 * expression structure like this, and a parse-time change of
997 * collation ought to be signaled by a CollateExpr not a RelabelType
998 * (the use of RelabelType for collation marking is supposed to be a
999 * planner/executor thing only). But we have no better alternative.
1000 * In particular, injecting a CollateExpr could result in the
1001 * expression being interpreted differently after dump/reload, since
1002 * we might be effectively promoting an implicit collation to
1003 * explicit. This kluge is relying on ruleutils.c not printing a
1004 * COLLATE clause for a RelabelType, and probably on some other
1005 * fragile behaviors.
1006 */
1007 if (OidIsValid(paircontext.collation) &&
1008 paircontext.collation != exprCollation((Node *) s_tle->expr))
1009 {
1010 s_tle->expr = (Expr *)
1011 makeRelabelType(s_tle->expr,
1012 exprType((Node *) s_tle->expr),
1013 exprTypmod((Node *) s_tle->expr),
1014 paircontext.collation,
1015 COERCE_IMPLICIT_CAST);
1016 }
1017
1018 /*
1019 * If appropriate, merge this column's collation state up to the
1020 * aggregate function.
1021 */
1022 if (merge_sort_collations)
1023 merge_collation_state(paircontext.collation,
1024 paircontext.strength,
1025 paircontext.location,
1026 paircontext.collation2,
1027 paircontext.location2,
1028 loccontext);
1029
1030 h_cell = lnext(h_cell);
1031 s_cell = lnext(s_cell);
1032 }
1033 Assert(h_cell == NULL && s_cell == NULL);
1034}
1035