Hi Hackers:
First I found the following queries running bad on pg.
select count(*) from part2 p1 where p_size > 40 and p_retailprice > (select avg(p_retailprice) from part2 p2 where p2.p_brand=p1.p_brand);
the plan is
QUERY PLAN
------------------------------------------------------------------------------------
Aggregate (cost=1899310537.28..1899310537.29 rows=1 width=8)
-> Seq Scan on part2 p1 (cost=0.00..1899310456.00 rows=32513 width=0)
Filter: ((p_size > 40) AND (p_retailprice > (SubPlan 1)))
SubPlan 1
-> Aggregate (cost=6331.00..6331.01 rows=1 width=32)
-> Seq Scan on part2 p2 (cost=0.00..5956.00 rows=150000 width=4)
Filter: (p_brand = p1.p_brand)
however if we change it to the following format, it runs pretty quick.
select count(*) from part2,
(select p_brand, avg(p_retailprice) as avg_price from part2 where p_size > 40 group by p_brand) p2
where p_retailprice > p2.avg_price
and p_size > 40
and part2.p_brand = p2.p_brand;
1. why pg can't translate the query 1 to query 2. after some checking on pull_up_sublinks_qual_recurse, I still doesn't get the idea.
2. why pg can't do it, while greenplum can?
Thanks
add the sql I used for testing for reference.
CREATE TABLE part2 (
p_partkey integer NOT NULL,
p_brand character(10) NOT NULL,
p_size integer NOT NULL,
p_retailprice numeric(15,2) NOT NULL
);
insert into part2 select 1, 'brand1', random_between(0, 40), random_between(0, 40) from generate_series(1, 100000);
insert into part2 select 2, 'brand2', random_between(40, 80), random_between(0, 40) from generate_series(1, 100000);
insert into part2 select 3, 'brand1', random_between(0, 40), random_between(0, 40) from generate_series(1, 100000);
