Re: Query performance

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(at)gmail(dot)com>

>
>
> On Mon, Oct 12, 2009 at 12:21 PM, S Arvind <arvindwill(at)gmail(dot)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
>