Query performance

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)

Thanks,
Arvind S

"Many of lifes failure are people who did not realize how close they were to
success when they gave up."
-Thomas Edison