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Improve UniquePath logic to detect the case where the input is already

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known unique (eg, it is a SELECT DISTINCT ... subquery), and not do a
redundant unique-ification step.
This commit is contained in:
Tom Lane
2004-01-05 18:04:39 +00:00
parent cce442da6d
commit 5c74ce23db
6 changed files with 72 additions and 15 deletions
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17
src/backend/optimizer/util/clauses.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.159 2004/01/04 03:51:52 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.160 2004/01/05 18:04:39 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@@ -921,6 +921,21 @@ has_distinct_on_clause(Query *query)
return false;
}
/*
* Test whether a query uses simple DISTINCT, ie, has a distinct-list that
* is the same as the set of output columns.
*/
bool
has_distinct_clause(Query *query)
{
/* Is there a DISTINCT clause at all? */
if (query->distinctClause == NIL)
return false;
/* It's DISTINCT if it's not DISTINCT ON */
return !has_distinct_on_clause(query);
}
/*****************************************************************************
* *