subselect and optimizer

Hi,

This question was sent to me by a user who uses PostgreSQL 6.3.1.
Is this normal?
(Note that the patch for src/backend/optimizer/path/prune.c created by
Vadim did not help)
--
Tatsuo Ishii
t-ishii(at)sra(dot)co(dot)jp
------------------------------------------------------------------
The following query seems to generate a rather slow query plan.

explain select * from product,order_tbl where
product.serial=order_tbl.serial and product.serial in (select serial
from order_tbl where cust_id='ABCDE');

NOTICE: QUERY PLAN:

Hash Join (cost=906.09 size=744 width=110)
-> Seq Scan on order_tbl (cost=296.13 size=6822 width=36)
-> Hash (cost=0.00 size=0 width=0)
-> Seq Scan on product (cost=358.29 size=744 width=74)
SubPlan
-> Index Scan on order_tbl (cost=2.05 size=1 width=12)

EXPLAIN

product and order_tbl are defined as follows:

create table product (
serial char(10) primary key,
pname char(15) not null,
price int2);
create index prod_name on product using hash(pname);

create table order_tbl (
cust_id char(5) primary key,
serial char(10) not null,
nums int2,
o_date date);
create index order_ser on order_tbl using hash(serial);

* product has 7289 tuples, and order_tbl has 6818 tuples.