Question

我正在处理一个SQL查询，在该查询中我想根据一个字段的最频繁出现将两个表联接在一起。

有一个我想从中获得最频繁订单的特定餐厅的餐厅表。这些食物可由同一家餐厅的多个不同的人订购。我想获得每个餐厅中最常出现的商品的结果，并且想要该商品中最常请求的人。

appveyor

我想要的，

||

我目前有以下脚本：

Table Restaurants  
Restaurant
=======
R1
R2 

Table Orders
Item    RequestedBy    Restaurant     Date
==========================================
B1          A           R1             123
B1          B           R1             234
B2          C           R2             456
B1          A           R1             567

当前返回的数据如下：

Restaurant  Item   RequestedBy
============================
 R1          B1        A
 R2          B2        C

任何帮助将不胜感激！谢谢

Answer 1

假设给定的Orders表包含一些不合适的数据，并且请求将按照描述进行查找

“以获取每个餐厅中最常出现的商品的结果” 然后进入

“我想要最常提出要求的人”

我建议保持其简单性，并在视图中拆分任务，例如

Create View V_OrdersPerRestaurant_Item as
Select Restaurant,Item, COUNT(*) as Orders
from [dbo].[orders]
group by Restaurant,Item


Create View V_MaxSelectItemPerRestaurant as
Select * from V_OrdersPerRestaurant_Item ov
where Orders = (Select Max(Orders) from V_OrdersPerRestaurant_Item where  ov.Restaurant=Restaurant)


Create View V_MaxSelectItemPerRestaurantAndRequestedBy as
Select ms.Item,ms.Restaurant,o.RequestedBy,Count(*) as Requests from V_MaxSelectItemPerRestaurant ms
join [dbo].[orders] o on ms.Item=o.Item and ms.Restaurant=o.Restaurant
group by ms.Item,ms.Restaurant,o.RequestedBy

应允许通过以下方式获得预期结果：

Select * from  V_MaxSelectItemPerRestaurantAndRequestedBy ov
where Requests=(Select max(Requests) from V_MaxSelectItemPerRestaurantAndRequestedBy iv where iv.Item=ov.Item and ov.Restaurant=iv.Restaurant)

Answer 2

我认为最简单的方法是使用apply：

select r.restaurant, ri.item, rir.requestedby
from restaurant r cross apply
     (select top (1) o.item, count(*) as cnt
      from orders o
      where o.restaurant = r.restaurant
      order by count(*) desc
     ) ri cross apply
     (select top (1) o2.requrestedby, count(*) as cnt
      from orders o2
      where o2.restaurant = r.restaurant and
            o2.item = r.item
      order by count(*) desc
     ) rir;

另一种可行的方法是使用窗口功能的order by：

select top (1) with ties restaurant, item, requestedby
from (select o.restaurant, o.item, o.requestedby,
             count(*) as rir_cnt,
             sum(count(*)) over (partition by o.restaurant, o.item) as ri_cnt
      from orders o
      group by o.restaurant, o.item, o.requestedby
     ) rir
order by row_number() over (partition by restaurant order by ri_cnt desc),
         row_number() over (partition by restaurant, item order by rir_cnt desc);

SQL查询：联接表中最频繁的值

2 个答案: