fanfuxiaoran commented on code in PR #685:
URL: https://github.com/apache/cloudberry/pull/685#discussion_r1858194701
##########
src/backend/optimizer/plan/transform.c:
##########
@@ -520,3 +521,134 @@ replace_sirvf_rte(Query *query, RangeTblEntry *rte)
return rte;
}
+
+/*
+ * Does query has SRFs, or WITH ORDINALITY?
+ */
+bool query_has_srf(Query *query)
+{
+ if (query->hasTargetSRFs)
+ {
+ return true;
+ }
+
+ /* Double check for subquery. */
+ if (expression_returns_set( (Node *) query->targetList))
+ {
+ return true;
+ }
+
+ ListCell *lcrte = NULL;
+ foreach (lcrte, query->rtable)
+ {
+ RangeTblEntry *rte = (RangeTblEntry *) lfirst(lcrte);
+
+ switch(rte->rtekind)
+ {
+ case RTE_FUNCTION:
+ {
+ ListCell *lcrtfunc;
+
+ /* WITH ORDINALITY */
+ if (rte->funcordinality)
+ return true;
+
+ foreach(lcrtfunc, rte->functions)
+ {
+ RangeTblFunction *rtfunc =
(RangeTblFunction *) lfirst(lcrtfunc);
+
+ if (!IsA(rtfunc->funcexpr, FuncExpr))
+ return true;
+
+ if (((FuncExpr *)
rtfunc->funcexpr)->funcretset)
+ {
+ /* SRF in FROM clause */
+ return true;
+ }
+ }
+ break;
+ }
+ case RTE_SUBQUERY:
+ {
+ Query *sq = (Query *) rte->subquery;
+
+ if (query_has_srf(sq))
+ {
+ return true;
+ }
+ break;
+ }
+ default:
+ {
+ break;
+ }
+ }
+ }
+
+ return false;
+}
+
+/*
+ * DISTINCT/DISTINCT ON/ORDER BY optimization.
+ * Remove DISTINCT clause if possibile, ex:
+ * select DISTINCT count(a) from t; to
+ * select count(a) from t;
+ * There is one row returned at most, DISTINCT and/or ON is pointless then.
+ * The same with ORDER BY clause;
+ */
+Query *remove_distinct_sort_clause(Query *parse)
+{
+ if (parse->hasAggs &&
+ parse->groupClause == NIL &&
+ !contain_mutable_functions((Node *) parse) &&
+ !query_has_srf(parse))
+ {
+ List *useless_tlist = NIL;
+ List *tles;
+ List *sortops;
+ List *eqops;
+ ListCell *lc;
+
+ if (parse->distinctClause != NIL)
Review Comment:
Hmm... If I understand correctly, `query_has_srf` doesn't need to care about
subquery or child nodes, it only need to check if the targetlist contains any
srf. (the targetlis which contains distinct expression).
But for `remove_distinct_sort_clause`, seems it only process the topmost
targetlist, subqueries are not processed
such as :
```
select * from t, (select distinct(count(*) from t);
```
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