Re: Query planner question

On Wed, Aug 20, 2014 at 6:16 PM, Soni M <diptatapa(at)gmail(dot)com> wrote:

> Hi Everyone,
>
> I have this query :
>
> select t.ticket_id ,
> tb.transmission_id
> from ticket t,
> transmission_base tb
> where t.latest_transmission_id = tb.transmission_id
> and t.ticket_number = tb.ticket_number
> and tb.parse_date > ('2014-07-31');
>
> Execution plan: http://explain.depesz.com/s/YAak
>
> Indexes on ticket :
> "ticket_pkey" PRIMARY KEY, btree (ticket_id) CLUSTER
> "ticket_by_latest_transmission" btree (latest_transmission_id)
> "ticket_by_ticket_number" btree (ticket_number)
>
> This query only returns some portions of rows from ticket table.
> The question is, Why does postgres need to get all the rows from ticket
> table in order to complete this query?
> Can't postgres use indexes to get only needed rows on ticket table?
>
> I try set seqscan to off, but still index scan try to get all rows on
> ticket table.
> Here's the execution plan : http://explain.depesz.com/s/abH2
>

If you want to force a nested loop, you probably need to disable the
mergejoin as well, and maybe the hashjoin. Forcing the planner to do
things the way you want can be difficult.

Cheers,

Jeff