I can understand left join, actually can any one tell me why sort operation is carried out and wat Materialize means... Can anyone explain me the mentioned plan with reason(s)?
-Arvind S 2009/10/12 Grzegorz Jaśkiewicz <gryz...@gmail.com> > > > 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 >
