我写了一条sql语句查询northwind数据库一年每个季度的销售情况，可是结果每年每季度的结果都是一样的

我写了一条sql语句查询northwind数据库一年每个季度的销售情况，可是结果每年每季度的结果都是一样的
select year(ShippedDate) as 年份,
第一季度=(select sum(UnitPrice*Quantity*(1-Discount))
from Orders,[Order Details]
where Orders.OrderID=[Order Details].OrderID
and month(ShippedDate) in (1,2,3)) ,
第二季度=(select sum(UnitPrice*Quantity*(1-Discount))
from Orders,[Order Details]
where Orders.OrderID=[Order Details].OrderID
and month(ShippedDate) in (4,5,6)),
第三季度=(select sum(UnitPrice*Quantity*(1-Discount))
from Orders,[Order Details]
where Orders.OrderID=[Order Details].OrderID
and month(ShippedDate) in (7,8,9)),
第四季度=(select sum(UnitPrice*Quantity*(1-Discount))
from Orders,[Order Details]
where Orders.OrderID=[Order Details].OrderID
and month(ShippedDate) in (10,11,12))
from Orders,[Order Details]
where year(ShippedDate) is not null
group by year(ShippedDate)
order by year(ShippedDate)
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