with x (id, date, value)
as (
values( 1 ,'20.06.11'::date, 4 )
union all
values( 2 ,'20.06.11'::date, 5 )
union all
values( 1 ,'21.06.11'::date, 2 )
union all
values( 2 ,'21.06.11'::date, 6 )
union all
values( 3 ,'22.06.11'::date, 8 )
)

select 
	id, 
	sum(first_dates) as first_dates,
	sum(last_dates) as last_dates
from (
	select
		id,
		case
			when date='2011-06-20' or date='2011-06-21'
			then value
			else  0 
		end as first_dates
		,
		case 
			when date='2011-06-22'
			then value
			else  0 
		end as last_dates
	from x
) as _t
group by id