[Answer Query Using Materialized Views] Support Postgres special grammar DISTINCT ON clause on origin query.

src/backend/optimizer/README.cbdb.aqumv

@@ -228,7 +228,7 @@ Below are not supported now:
       Window Functions
       CTE
       Distinct (on view_query)
-      Distinct On
+      Distinct On (on view_query)
       UNION/INTERSECT/EXCEPT
       FOR UPDATE, FOR NO KEY UPDATE, FOR SHARE, FOR KEY SHARE
       Scatter By

src/backend/optimizer/plan/aqumv.c

@@ -119,7 +119,6 @@ answer_query_using_materialized_views(PlannerInfo *root,
 						  (parse->cteList != NIL) ||
 						  (parse->setOperations != NULL) ||
 						  parse->hasWindowFuncs ||
-						  parse->hasDistinctOn ||
 						  parse->hasModifyingCTE ||
 						  (parse->parentStmtType == PARENTSTMTTYPE_REFRESH_MATVIEW) ||
 						  (parse->parentStmtType == PARENTSTMTTYPE_CTAS) ||
@@ -328,6 +327,7 @@ answer_query_using_materialized_views(PlannerInfo *root,
 		 * could be computed from viewQuery.
 		 */
 		viewQuery->hasAggs = parse->hasAggs;
+		viewQuery->hasDistinctOn = parse->hasDistinctOn;
 		/*
 		 * For HAVING quals have aggregations, we have already processed them in
 		 * Aggrefs during aqumv_process_targetlist().

src/test/regress/expected/aqumv.out

@@ -2084,6 +2084,84 @@ select c1, c2, c3, sum(c4) from aqumv_t6 where c1 > 97 group by distinct rollup(
    98 | NULL |  100 | 202
 (13 rows)
 
+-- DISTINCT ON
+set local enable_answer_query_using_materialized_views = off;
+explain(costs off, verbose)
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+                                    QUERY PLAN                                     
+-----------------------------------------------------------------------------------
+ Gather Motion 3:1  (slice1; segments: 3)
+   Output: c1, c2, ((c1 - 1))
+   Merge Key: ((c1 - 1)), c2
+   ->  Unique
+         Output: c1, c2, ((c1 - 1))
+         Group Key: ((c1 - 1))
+         ->  Sort
+               Output: c1, c2, ((c1 - 1))
+               Sort Key: ((aqumv_t6.c1 - 1)), aqumv_t6.c2 NULLS FIRST
+               ->  Redistribute Motion 3:3  (slice2; segments: 3)
+                     Output: c1, c2, ((c1 - 1))
+                     Hash Key: ((c1 - 1))
+                     ->  Seq Scan on public.aqumv_t6
+                           Output: c1, c2, (c1 - 1)
+                           Filter: (aqumv_t6.c1 > 90)
+ Settings: enable_answer_query_using_materialized_views = 'off', optimizer = 'off'
+ Optimizer: Postgres query optimizer
+(17 rows)
+
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+ c1  |  c2  
+-----+------
+  91 | NULL
+  92 |   93
+  93 |   94
+  94 |   95
+  95 |   96
+  96 |   97
+  97 |   98
+  98 |   99
+  99 |  100
+ 100 |  101
+(10 rows)
+
+set local enable_answer_query_using_materialized_views = on;
+explain(costs off, verbose)
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+                                    QUERY PLAN                                    
+----------------------------------------------------------------------------------
+ Gather Motion 3:1  (slice1; segments: 3)
+   Output: mc1, mc2, ((mc1 - 1))
+   Merge Key: ((mc1 - 1)), mc2
+   ->  Unique
+         Output: mc1, mc2, ((mc1 - 1))
+         Group Key: ((mc1 - 1))
+         ->  Sort
+               Output: mc1, mc2, ((mc1 - 1))
+               Sort Key: ((aqumv_mvt6_0.mc1 - 1)), aqumv_mvt6_0.mc2 NULLS FIRST
+               ->  Redistribute Motion 3:3  (slice2; segments: 3)
+                     Output: mc1, mc2, ((mc1 - 1))
+                     Hash Key: ((mc1 - 1))
+                     ->  Seq Scan on public.aqumv_mvt6_0
+                           Output: mc1, mc2, (mc1 - 1)
+ Settings: enable_answer_query_using_materialized_views = 'on', optimizer = 'off'
+ Optimizer: Postgres query optimizer
+(16 rows)
+
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+ c1  |  c2  
+-----+------
+  91 | NULL
+  92 |   93
+  93 |   94
+  94 |   95
+  95 |   96
+  96 |   97
+  97 |   98
+  98 |   99
+  99 |  100
+ 100 |  101
+(10 rows)
+
 \pset null ''
 abort;
 reset optimizer;

src/test/regress/sql/aqumv.sql

@@ -514,6 +514,16 @@ explain(costs off, verbose)
 select c1, c2, c3, sum(c4) from aqumv_t6 where c1 > 97 group by distinct rollup(c1, c2), rollup(c1, c3);
 select c1, c2, c3, sum(c4) from aqumv_t6 where c1 > 97 group by distinct rollup(c1, c2), rollup(c1, c3);
 
+-- DISTINCT ON
+set local enable_answer_query_using_materialized_views = off;
+explain(costs off, verbose)
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+set local enable_answer_query_using_materialized_views = on;
+explain(costs off, verbose)
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+select distinct on(c1 - 1) c1, c2 from aqumv_t6 where c1 > 90 order by c1 - 1, c2 nulls first;
+
 \pset null ''
 abort;