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
<gryzman@gmail.com>
On Mon, Oct 12, 2009 at 12:21 PM, S Arvind
<arvindwill@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
