diff options
Diffstat (limited to 'src/backend/optimizer/plan/analyzejoins.c')
| -rw-r--r-- | src/backend/optimizer/plan/analyzejoins.c | 28 |
1 files changed, 14 insertions, 14 deletions
diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c index 5b0da14748a..5783f90b62e 100644 --- a/src/backend/optimizer/plan/analyzejoins.c +++ b/src/backend/optimizer/plan/analyzejoins.c @@ -744,8 +744,8 @@ rel_is_distinct_for(PlannerInfo *root, RelOptInfo *rel, List *clause_list) bool query_supports_distinctness(Query *query) { - /* we don't cope with SRFs, see comment below */ - if (query->hasTargetSRFs) + /* SRFs break distinctness except with DISTINCT, see below */ + if (query->hasTargetSRFs && query->distinctClause == NIL) return false; /* check for features we can prove distinctness with */ @@ -787,20 +787,10 @@ query_is_distinct_for(Query *query, List *colnos, List *opids) Assert(list_length(colnos) == list_length(opids)); /* - * A set-returning function in the query's targetlist can result in - * returning duplicate rows, if the SRF is evaluated after the - * de-duplication step; so we play it safe and say "no" if there are any - * SRFs. (We could be certain that it's okay if SRFs appear only in the - * specified columns, since those must be evaluated before de-duplication; - * but it doesn't presently seem worth the complication to check that.) - */ - if (query->hasTargetSRFs) - return false; - - /* * DISTINCT (including DISTINCT ON) guarantees uniqueness if all the * columns in the DISTINCT clause appear in colnos and operator semantics - * match. + * match. This is true even if there are SRFs in the DISTINCT columns or + * elsewhere in the tlist. */ if (query->distinctClause) { @@ -820,6 +810,16 @@ query_is_distinct_for(Query *query, List *colnos, List *opids) } /* + * Otherwise, a set-returning function in the query's targetlist can + * result in returning duplicate rows, despite any grouping that might + * occur before tlist evaluation. (If all tlist SRFs are within GROUP BY + * columns, it would be safe because they'd be expanded before grouping. + * But it doesn't currently seem worth the effort to check for that.) + */ + if (query->hasTargetSRFs) + return false; + + /* * Similarly, GROUP BY without GROUPING SETS guarantees uniqueness if all * the grouped columns appear in colnos and operator semantics match. */ |