select c.Category, s.Total
FROM 
   (select c1.Category from Categories c1 group by Category) c
left join 
   (select sum(price) as Total, category from sales where saledate between @StartDate1 and @EndDate1) s
on c.Category = s.Category
group by c.Category

SELECT * FROM (VALUES (@From1,@To1),(@From2,@To2)) X([From],[To])
JOIN .. ON D >= X.[From] AND D < X.[To]

select
  C.Category,
  sum(case when S.saledate between @StartDate1 and @EndDate1 then S.price else 0 end) as Total1,
  sum(case when S.saledate between @StartDate2 and @EndDate2 then S.price else 0 end) as Total2
FROM Categories C
  inner join sales S on S.Category = C.Category
group by
  C.Category