fanfuxiaoran commented on code in PR #685:
URL: https://github.com/apache/cloudberry/pull/685#discussion_r1868614781
##########
src/backend/optimizer/plan/transform.c:
##########
@@ -520,3 +522,87 @@ replace_sirvf_rte(Query *query, RangeTblEntry *rte)
return rte;
}
+
+/*
+ * Does target list have SRFs?
+ */
+static
+bool tlist_has_srf(Query *query)
+{
+ if (query->hasTargetSRFs)
+ {
+ return true;
+ }
+
+ if (expression_returns_set( (Node *) query->targetList))
+ {
+ return true;
+ }
+
+ 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) &&
+ !tlist_has_srf(parse))
+ {
+ List *useless_tlist = NIL;
+ List *tles;
+ List *sortops;
+ List *eqops;
+ ListCell *lc;
+
+ if (parse->distinctClause != NIL)
+ {
Review Comment:
Yes, this looks good, not a big deal.
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