On Mon, Oct 12, 2009 at 12:21 PM, S Arvind <arvindwill@xxxxxxxxx> wrote:
In the below query both table has less than 1 million data. Can u tell me the reason of this plan?
why its takin extensive cost , seq scan and sorting?? wat is Materialize?
select 1 from service_detail
left join non_service_detail on non_service_detail_service_id = service_detail.service_detail_id
Merge Left Join (cost=62451.86..67379.08 rows=286789 width=0)
Merge Cond: (service_detail.service_detail_id = non_service_detail.non_service_detail_service_id)
-> Sort (cost=18610.57..18923.27 rows=125077 width=8)
Sort Key: service_detail.service_detail_id
-> Seq Scan on service_detail (cost=0.00..6309.77 rows=125077 width=8)
-> Materialize (cost=43841.28..47426.15 rows=286789 width=8)
-> Sort (cost=43841.28..44558.26 rows=286789 width=8)
Sort Key: non_service_detail.non_service_detail_service_id
-> Seq Scan on non_service_detail (cost=0.00..13920.89 rows=286789 width=8)
A) it is a left join, meaning - everything is pulled from left side,
B) there are no conditions, so ... ... everything is pulled again from left side.
B) there are no conditions, so ... ... everything is pulled again from left side.
--
GJ
