Если 8,4 +:
select
a::date as Sunday,
a::date - 1 as Saturday
from generate_series('2000-01-02'::date, '2050-12-31', '7 days') s(a)
;
прочее:
select
'2000-01-02'::date + s.a as Sunday,
'2000-01-02'::date + s.a - 1 as Saturday
from generate_series(0, '2050-12-31'::date - '2000-01-02'::date, 7) s(a)
;