On Mon, Oct 12, 2009 at 12:21 PM, S Arvind <arvindw...@gmail.com> 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. -- GJ
