recreate table test_grouping (
  id integer,
  caption varchar(50),
  val double precision
)


execute block
as
declare variable i int;
begin
  i = 100000;
  while (i>0) do
  begin
   insert into TEST_GROUPING (ID, CAPTION, VAL)
      values (:i, 'VALUE FOR TEST'||:i, 1);
   insert into TEST_GROUPING (ID, CAPTION, VAL)
      values (:i, 'VALUE FOR TEST'||:i, 2);
   insert into TEST_GROUPING (ID, CAPTION, VAL)
      values (:i, 'VALUE FOR TEST'||:i, 3);
    i = i - 1;
  end
end


select val, sum(val), count(val) from
(
    select * from  test_grouping
    union all
    select * from  test_grouping
    union all
    select * from  test_grouping
)
group by val
-- Execute time = 1s 966ms
/*
Select Expression
    -> Aggregate
        -> Sort (record length: 116, key length: 12)
            -> Union
                -> Table "TEST_GROUPING" Full Scan
                -> Table "TEST_GROUPING" Full Scan
                -> Table "TEST_GROUPING" Full Scan
*/

select val, sum(val), count(val) from
(
    select val from  test_grouping
    union all
    select val from  test_grouping
    union all
    select val from  test_grouping
)
group by val
-- Execute time = 1s 513ms
/*
Select Expression
    -> Aggregate
        -> Sort (record length: 60, key length: 12)
            -> Union
                -> Table "TEST_GROUPING" Full Scan
                -> Table "TEST_GROUPING" Full Scan
                -> Table "TEST_GROUPING" Full Scan
*/

select val, sum(val), count(val) from
(
    select val, sum(val) as summa, count(*) as cnt from  test_grouping
    group by val
    union all
    select val, sum(val) as summa, count(*) as cnt from  test_grouping
    group by val
    union all
    select val, sum(val) as summa, count(*) as cnt from  test_grouping
    group by val
)
group by val
-- Execute time = 1s 170ms