Re: Selection of join algorithm

If you specify joining condition other than equality then nested loop join
is invoked.
Example Query : explain analyze select name from student,takes where
student.id > takes.id

If both the input to join is sorted on joining condition then merge join is
invoked.
Example Query: explain analyze select stud.name from (select id, name from
student order by id) stud,(select id,year from takes order by id) t where
stud.id = t.id

On Sat, Mar 8, 2014 at 7:50 PM, Ishaya Bhatt <ishayabhatt(at)gmail(dot)com> wrote:

> Hi,
>
> I am trying to analyze join performance. But I see that even for a table
> having 100,000 rows and join attribute as primary key, postgres always
> performs hash join.
>
> Can anyone please tell me under which conditions merge join or nested loop
> join is invoked?
>
> Thanks and Regards,
> Ishaya
>