[Answer Query Using Materialized Views] Support HAVING clause in origin query

[avamingli]

Support HAVING clause of origin query if it could be computed from materialized views.

create incremental materialized view mv as
  select c1 as mc1, c2 as mc2, c3 as mc3
  from t1 where c1 > 90;

Origin query:

  select c1, c3, avg(c2) from t1 where c1 > 90
  group by (c1, c3) having avg(c2) > 95;

Could be rewritten to:

  select mc1, mc3, avg(mc2) from mv
  group by (mc1, mc3) having avg(mc2) > 95;

For HAVING quals don't have aggregations, they may be pushed down to jointree's quals and would be processed in post_quals.

DDL:

create table aqumv_t4(c1 int, c2 int, c3 int) distributed by (c1);
insert into aqumv_t4 select i, i+1, i+2 from generate_series(1, 100) i;
insert into aqumv_t4 values (91, NULL, 95);
analyze aqumv_t4;
create incremental materialized view aqumv_mvt4_0 as
  select c1 as mc1, c2 as mc2, c3 as mc3
  from aqumv_t4 where c1 > 90;
analyze aqumv_mvt4_0;

begin;
-- HAVING clause pushed down to where quals.
set local enable_answer_query_using_materialized_views = off;
explain(costs off, verbose)
select c1, c3 from aqumv_t4 where c1 > 90 group by (c1, c3) having c3 > 97 ;
                                    QUERY PLAN                                     
-----------------------------------------------------------------------------------
 Gather Motion 3:1  (slice1; segments: 3)
   Output: c1, c3
   ->  GroupAggregate
         Output: c1, c3
         Group Key: aqumv_t4.c1, aqumv_t4.c3
         ->  Sort
               Output: c1, c3
               Sort Key: aqumv_t4.c1, aqumv_t4.c3
               ->  Seq Scan on public.aqumv_t4
                     Output: c1, c3
                     Filter: ((aqumv_t4.c1 > 90) AND (aqumv_t4.c3 > 97))
 Settings: enable_answer_query_using_materialized_views = 'off', optimizer = 'off'
 Optimizer: Postgres query optimizer
(13 rows)
set local enable_answer_query_using_materialized_views = on;
explain(costs off, verbose)
select c1, c3 from aqumv_t4 where c1 > 90 group by (c1, c3) having c3 > 97 ;
                                    QUERY PLAN                                    
----------------------------------------------------------------------------------
 Gather Motion 3:1  (slice1; segments: 3)
   Output: mc1, mc3
   ->  HashAggregate
         Output: mc1, mc3
         Group Key: aqumv_mvt4_0.mc1, aqumv_mvt4_0.mc3
         ->  Seq Scan on public.aqumv_mvt4_0
               Output: mc1, mc2, mc3
               Filter: (aqumv_mvt4_0.mc3 > 97)
 Settings: enable_answer_query_using_materialized_views = 'on', optimizer = 'off'
 Optimizer: Postgres query optimizer
(10 rows)
end;

For HAVING quals have aggregations, we process them in Aggrefs of target list.

explain(costs off, verbose)
select c1, c3, avg(c2) from aqumv_t4 where c1 > 90 group by (c1, c3) having avg(c2) > 95;
                                    QUERY PLAN                                    
----------------------------------------------------------------------------------
 Gather Motion 3:1  (slice1; segments: 3)
   Output: mc1, mc3, (avg(mc2))
   ->  HashAggregate
         Output: mc1, mc3, avg(mc2)
         Group Key: aqumv_mvt4_0.mc1, aqumv_mvt4_0.mc3
         Filter: (avg(aqumv_mvt4_0.mc2) > '95'::numeric)
         ->  Seq Scan on public.aqumv_mvt4_0
               Output: mc1, mc2, mc3
 Settings: enable_answer_query_using_materialized_views = 'on', optimizer = 'off'
 Optimizer: Postgres query optimizer
(10 rows)

Authored-by: Zhang Mingli avamingli@gmail.com

fix #ISSUE_Number

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[yjhjstz]

LGTM