如果所有符合相同条件并且只有一个符合条件，则选择行

Question

我有一个OrdersDetails表，所以我希望根据订单状态获取订单状态，当所有产品都是新产品然后状态是新的，当所有产品都关闭然后状态关闭，当某些产品待处理时状态正在等待。

OrderId     |ProductID   |ProductStatus
ORDER1      |PRODUCT1    |NEW
ORDER1      |PRODUCT2    |PENDING
ORDER2      |PRODUCT3    |CLOSED
ORDER2      |PRODUCT4    |CLOSED
ORDER3      |PRODUCT5    |NEW
ORDER3      |PRODUCT6    |NEW
ORDER4      |PRODUCT7    |CLOSED
ORDER4      |PRODUCT8    |PENDING

期望的结果表

OrderID  |Status
ORDER1   |PENDING
ORDER2   |CLOSED
ORDER3   |NEW
ORDER4   |PENDING

Answer 1

这是group by case：

select orderid,
       (case when min(status) = max(status) and min(status) in ('NEW', 'CLOSED')
             then min(status)
             when sum(case when status = 'PENDING' then 1 else 0 end) > 0
             then 'PENDING'
             else 'This case is not described in the question'
        end)
from t
group by orderid;

Answer 2

假设你永远不会得到混合状态，除非订单有待处理，这应该有效：

select OrderId, 'PENDING' Status
from #orderTable
group by OrderId
having COUNT(distinct ProductStatus)>1
union all
select OrderId, MIN(ProductStatus) Status
from #orderTable
group by OrderId
having COUNT(distinct ProductStatus)=1
order by 1