BUG #1241: returns different result for the same result with differnt plans.

The following bug has been logged online:

Bug reference: 1241
Logged by: Xiaoyu Wang

Email address: wangxy(at)cs(dot)brandeis(dot)edu

PostgreSQL version: 7.4.3

Operating system: Mandrake Linux 9.2 3.3.1-2mdk

Description: returns different result for the same result with
differnt plans.

Details:

database: TPC-H with scale factor=1.0
query: 13.sql (TPC-H)

select
c_count,
count(*) as custdist
from
(
select
c_custkey,
count(o_orderkey)
from
customer left outer join orders on
c_custkey = o_custkey
and o_comment not like '%special%requests'
group by
c_custkey
) as c_orders (c_custkey, c_count)
group by
c_count
order by
custdist desc,
c_count desc;

I ran the query with enable_mergejoin set to on/off, the results are
different. Postgres chose Merge Left Join when enable_mergejoin is on and
Hash Left Join when it is off. I dumped the results to two files, merge.data
and hash.data. Here is the result when I do a diff:

diff merge.data hash.data
3d2
< 0 | 50004
41a41
> 0 | 4