|
8 | 8 | * |
9 | 9 | * |
10 | 10 | * IDENTIFICATION |
11 | | - * $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.99 2004/01/05 23:39:54 tgl Exp $ |
| 11 | + * $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.100 2004/01/19 03:49:41 tgl Exp $ |
12 | 12 | * |
13 | 13 | *------------------------------------------------------------------------- |
14 | 14 | */ |
|
33 | 33 | #include"utils/syscache.h" |
34 | 34 |
|
35 | 35 |
|
| 36 | +staticboolis_distinct_query(Query*query); |
36 | 37 | staticboolhash_safe_tlist(List*tlist); |
37 | 38 |
|
38 | 39 |
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@@ -553,16 +554,14 @@ create_unique_path(Query *root, RelOptInfo *rel, Path *subpath) |
553 | 554 | pathnode->subpath=subpath; |
554 | 555 |
|
555 | 556 | /* |
556 | | - * If the input is a subquery that uses DISTINCT, we don't need to do |
557 | | - * anything; its output is already unique. (Are there any other cases |
558 | | - * in which we can easily prove the input must be distinct?) |
| 557 | + * If the input is a subquery whose output must be unique already, |
| 558 | + * we don't need to do anything. |
559 | 559 | */ |
560 | 560 | if (rel->rtekind==RTE_SUBQUERY) |
561 | 561 | { |
562 | 562 | RangeTblEntry*rte=rt_fetch(rel->relid,root->rtable); |
563 | | -Query*subquery=rte->subquery; |
564 | 563 |
|
565 | | -if (has_distinct_clause(subquery)) |
| 564 | +if (is_distinct_query(rte->subquery)) |
566 | 565 | { |
567 | 566 | pathnode->umethod=UNIQUE_PATH_NOOP; |
568 | 567 | pathnode->rows=rel->rows; |
@@ -667,6 +666,36 @@ create_unique_path(Query *root, RelOptInfo *rel, Path *subpath) |
667 | 666 | returnpathnode; |
668 | 667 | } |
669 | 668 |
|
| 669 | +/* |
| 670 | + * is_distinct_query - does query never return duplicate rows? |
| 671 | + */ |
| 672 | +staticbool |
| 673 | +is_distinct_query(Query*query) |
| 674 | +{ |
| 675 | +/* DISTINCT (but not DISTINCT ON) guarantees uniqueness */ |
| 676 | +if (has_distinct_clause(query)) |
| 677 | +return true; |
| 678 | + |
| 679 | +/* UNION, INTERSECT, EXCEPT guarantee uniqueness, except with ALL */ |
| 680 | +if (query->setOperations) |
| 681 | +{ |
| 682 | +SetOperationStmt*topop= (SetOperationStmt*)query->setOperations; |
| 683 | + |
| 684 | +Assert(IsA(topop,SetOperationStmt)); |
| 685 | +Assert(topop->op!=SETOP_NONE); |
| 686 | + |
| 687 | +if (!topop->all) |
| 688 | +return true; |
| 689 | +} |
| 690 | + |
| 691 | +/* |
| 692 | + * XXX Are there any other cases in which we can easily see the result |
| 693 | + * must be distinct? |
| 694 | + */ |
| 695 | + |
| 696 | +return false; |
| 697 | +} |
| 698 | + |
670 | 699 | /* |
671 | 700 | * hash_safe_tlist - can datatypes of given tlist be hashed? |
672 | 701 | * |
|